At the end of college most kids are still evolving. I witness this growth every day in my lab, where we take in college grads who are still undecided about whether they want to go to graduate school or medical school or whether they’d rather not pursue any postundergraduate degree at all and just get a full-time job out in the “real” world. They come in as bright, young students with excellent academic records to work as lab assistants. Their job is to help the other doctors and scientists with experiments and also keep the laboratory going with respect to cleaning and maintaining the equipment, and making sure orders are filled and meetings are scheduled. On entry, they embark on a steep learning curve concerning the science behind our work. However, the greater transformation they undergo comes subtly, as a result of having to communicate between lots of different types of people, organizing and prioritizing tasks, and knowing other people are counting on them. Over the course of two years or so, these young people really become adults; their sense of accountability and their communication skills in a professional environment are probably the greatest benefits they get from the whole experience. My own son Andrew did this very thing, leaving a physics master’s degree program to change fields and work in a lab in New York City not much different from mine. From the other side, I saw his work ethic grow and his ability to organize and multitask get better, and like the kids in my lab, he got a huge boost in confidence from succeeding in a “real world” job. It will serve him well as he now enters advanced degree work.

In my lab, this growth shines through when these young people are about to leave, especially in their interviews for graduate school, medical school, or a job in the workplace. It’s a joy for me to write their reference letters, and I marvel at the fact that this transformation happens, to at least some extent, to nearly every young person who spends a year or two in my lab. On occasion, some have brought their parents, who might be visiting from out of town, to the lab, and it gives me the greatest pleasure to tell them how proud they should be of their sons and daughters. Of course, I do manage to embarrass my young workforce this way!

What’s important to remember is that young adulthood is still a great time to learn. There remains a high amount of brain plasticity going on, while brain connectivity has improved and so has the ability to multitask. Many young adults find that their learning skills are much better at this age than when they were in high school. Organizational skills improve, as does the ability to abstract. Judgment, insight, and perspective all improve as a result of more accessible frontal lobes.

The fact that many kids take a gap year prior to college makes a lot of sense developmentally. In many countries the “gap year” concept is nationally mandated. A number of European countries actually have a national “year of service” for teenagers when high school ends. In Israel, both boys and girls are drafted into the army. The boys serve three years, the girls two, and although those from certain Orthodox Jewish groups are exempt because of religious restrictions, they often engage in some other form of national service. The gap year for young Israelis comes the year after military service is finished and before they go on to a university. During that year many young people travel to Asia, South America, and India before they begin their higher education.

We, too, now have an informal “gap year” in the United States with community service or volunteer internships, such as the AmeriCorps program City Year, and testimonials from young adults describe how their gap year was the most valuable year of their lives. I witnessed this myself with my son Will, who took a year off after graduating from high school to travel solo around the world and to work. During that time he spent the first six months learning to speak Spanish in an immersion course in South America and then spent the remaining six months as an employee of a Boston software firm. By the time he was ready to enter Harvard, he was more mature both emotionally and intellectually, and he has told me more than once that the experiences of his gap year were invaluable to him in his development.

Young adulthood as a distinct developmental stage continues to be debated by sociologists, psychologists, and scientists. In the middle of the twentieth century the psychologist Erik Erikson was one of the first to suggest that adulthood had stages, broken down roughly into the ages twenty to forty-five, forty-five to sixty-five, and sixty-five to death. But it was Kenneth Keniston who, in 1970, wrote a seminal yet rather forgotten research paper called “Youth: A ‘New’ Stage of Life.” In it, Keniston postulated that a person’s twenties—that is, the years between adolescence and young adulthood—were a distinct stage of development. Keniston was then a Yale psychologist, and he characterized this period chiefly as one of freedom, movement, change, and ambivalence. He also described a number of themes or issues that dominate this “youth” stage:

        • Tension between self and society

        • Pervasive ambivalence

        • Wary probe

        • Estrangement

        • Omnipotentiality

        • Refusal of socialization

        • Youth-specific identities

        • Movement

        • Abhorrence of stasis

        • Be moved/move through

        • Valuation of development

        • The fear of death

        • View of adulthood

        • Youthful countercultures

Keniston, who was writing about today’s aging baby boomers, said that here was “a growing minority of postadolescents [who] have not settled the questions whose answers once defined adulthood: questions of relationship to the existing society, questions of vocation, questions of social role and lifestyle.” The overriding characteristic of this “youth” stage, he said, was a “pervasive ambivalence toward self and society.” This is a good news–bad news story. The energy and novelty-seeking so characteristic of this developmental stage are highly adaptive and allow teenagers to explore new domains that could match their skill sets, yet this same behavior can expose them to risky environments. Their lack of life experience can fuel ambivalence and fear, but this is where the family and community can come together around adolescents to provide reassurance and structure as they build their own context for their life experience.

As it turns out, it was an accurate description of my generation, but Keniston’s theory of a postadolescent, preadult stage of life never really took hold—until psychologist Jeffrey Jensen Arnett wrote a book a decade ago called Emerging Adulthood: The Winding Road from the Late Teens Through the Twenties. Drawing on Keniston’s work, Arnett postulated a distinct stage he called “emerging adulthood,” mostly brought on by cultural and economic changes that have left twenty-somethings feeling insecure, needing more education, finding fewer jobs, resisting the rush to marry because of the acceptance of premarital sex, and delaying having children because of the sophistication of reproductive technology. The age of emerging adulthood is an age of exploration and instability, Arnett says, but today it’s also an age of self-involvement.

That’s certainly clear in the HBO series Girls, which features women in their twenties trying to figure out how to live, love, and succeed in New York City. It’s worlds away from Sex and the City, and though it’s billed as a comedy, there are plenty of uncomfortable and dramatic moments. The series was created in 2012 by then-twenty-six-year-old writer Lena Dunham, who also stars as the main character, an aspiring writer named Hannah. Early in the series, Hannah’s parents tell her they can no longer subsidize her apartment in Brooklyn. When she then asks her boss to be paid, she is essentially fired from her unpaid internship. Later, she fails as a clerk in a law office and finally must settle for a job in a coffee shop. Hannah’s life always seems to be in turmoil. She breaks up and makes up with her boyfriend multiple times and temporarily moves out of the apartment she shares with a female friend after they have an emotional disagreement. In other words, she’s a mess—psychologically, emotionally, romantically, and vocationally. She’s also not alone—hence the popularity of the series, especially among young women. In one episode, when she visits her upper-middle-class parents back in Michigan, Hannah catches up with a former friend, Heather, who tells her about her big dreams. Hannah is skeptical, but when she tells another friend about the conversation, it almost seems that she is talking about herself:

Hannah has moments of self-awareness, but they are few and far between. Instead, she and her friends vacillate about jobs, about men, about decisions both big and small in scenes that could just as easily be playing out among the approximately seventy million Americans who find themselves in this peculiar age, between eighteen and thirty-four, grown up and yet not quite grown up. The twenties are an age of self-absorption, of excitement and anxiety about the possibilities ahead, and especially of uncertainty—about jobs, careers, relationships; about who they are, where they’re going, and when they’ll get there. All across the developed world, young adults are trying to answer these questions. As they do, they are taking more time than ever before, at least in recent human history, to leave home, finish school, get married, and find a career. In some sense how do these kids not avoid being overly self-involved?

It’s true that for the millennial generation, those born between 1980 and 2000, the incidence of narcissistic personality disorder is three times what it is for those sixty-five and older, according to the National Institutes of Health. Not surprisingly, the Oxford English Dictionary designated “selfie,” those ubiquitous cell phone photos so many teens and young adults take of themselves, as its word of the year for 2013. In large part, many believe that the millennial generation’s apparent self-centeredness was created by its parents, who, by way of overpraising their children, pushed them to become more self-involved and self-important. By instilling “too much” self-confidence in their kids, says Roy Baumeister, who teaches psychology at Florida State University, these parents “accidentally” injected their kids with a heavy dose of narcissism and a sense of entitlement as well. So there is a fine balance to strike when it comes to providing an assuring context to teens’ experiences: too little and they feel lost, but too much and they are unrealistically confident, a setup for later problems in life.

On the positive side of the millennials’ ledger, there is much to praise. While they are not as idealistic as past generations, they are earnest, pragmatic, and even optimistic despite growing up in the shadow of 9/11, two wars, and a debilitating recession. In her book 20 Something Manifesto, Christine Hassler collects the reflections of postadolescent young adults who find this particular stage of their lives uniquely stressful. One twenty-five-year-old woman said it is “somewhat terrifying to think about all the things I’m supposed to be doing in order to ‘get somewhere’ successful: ‘Follow your passions, live your dreams, take risks, network with the right people, find mentors, be financially responsible, volunteer, work, think about or go to grad school, fall in love and maintain personal well-being, mental health and nutrition.’ When is there time to just be and enjoy?” Another twenty-five-year-old wrote, “Our culture really focuses on youth and success, and many of us feel that we have to be fabulously successful by age thirty or we’re failures.”

Laura Humphrey, a psychologist and director of Yellowbrick, a private psychiatric facility specializing in problems of emerging adulthood, describes the unique issues associated with the age group:

Statistics seem to bear out the underlying insecurity of young adulthood: A third of all Americans in their twenties move every year, and 40 percent move back in with their parents at least once after college. Young adults go through an average of seven changes in employment before turning thirty, and two-thirds live with a partner without getting married for at least a portion of their twenties. Arnett claims that 60 percent of the subjects he’s studied who are in their twenties say they feel both grown up and not quite grown up at the same time.

When your sons or daughters who are out of college and on their own seem unable to learn how to do laundry, create a budget, or set up utilities in a new apartment, remember, again, that while they’re no longer adolescents, white matter is still being laid down in their frontal lobes, wiring their brain systems together. Like adolescents, young adults are sometimes victims of their own still-changing brains. That white matter connectivity still taking place after adolescence also carries substantial dangers. White matter abnormalities in the frontal regions of the brain appear to play a part in psychiatric disorders that develop not just during adolescence but also in young adulthood. In fact, mental disorders are estimated to account for nearly half the total disease burden for young adults in the United States, according to the World Health Organization. In a recent study, researchers found that almost half of college students and their non-college-attending peers had met the criteria for a diagnosable mental illness in the previous year, with alcohol use disorders the most common. And yet much less is known about the potential risk factors of mental health problems for young adults than almost any other age group.

Abnormalities in white matter tracts involved in attention may also explain the frequency of adult ADHD, which usually first appears in childhood or adolescence but may have gone undiagnosed. From a quality-of-life standpoint, young adults with ADHD suffer considerable disruption of their daily lives. Studies have shown they achieve fewer educational goals beyond high school than young adults without ADHD symptoms, are less likely to be employed full-time, and have lower average household incomes. Other studies have found they are also twice as likely to get arrested or divorced, 78 percent more likely to be addicted to cigarettes or cigars, three times more likely to be out of work, and four times more likely to contract a sexually transmitted disease.

How vulnerable are emerging adults? The incarceration rate for young adults, ages twenty to twenty-four, nearly doubled over the last decade. Young adults with mental health issues are at higher risk of dropping out of college, having unplanned pregnancies, being unemployed, and suffering from drug and alcohol abuse. And yet the drop-off in mental health services from teenage years to young adulthood is drastic. More than twice as many teens as emerging adults receive inpatient or residential care. And this doesn’t include the fact that today we have a whole generation of war veterans in their twenties and thirties with special needs and problems, both physical and mental.

Young adults have not been forsaken, however. There are residential treatment centers for emerging adults like New Lifestyles in Winchester, Virginia; websites, like the Network on Transitions to Adulthood (transitions2adulthood.com), that address the specific concerns of postadolescent young adults; and books like Coming of Age in America: The Transition to Adulthood in the Twenty-First Century. There is even a Society for the Study of Emerging Adulthood and a scholarly journal dedicated to this discrete age group.

With the neuroscience of young adulthood still in its infancy, we don’t yet know if the twenties represent a last chance to capitalize on the final stage of brain development; whether, as parents or scientists or educators, we should be urging twentysomethings to find a skilled job—any job—before their learning curves begin their slow dive with aging or whether we should urge the opposite, to take a final fling at exploring possibilities while creative thinking is still at its neurobiological height. Jay Giedd, the NIMH scientist who has been studying the teenage brain longer than almost anyone else, told a reporter, “It’s too soon to tell.” But if we’ve learned anything about neuroscience in the past decade, then maybe the answer should be “Stay tuned.”