In a time when college graduates return to live under their parents’ roofs and top careers require years of internships and graduate degrees, the age of adulthood is receding, practically into the 30s. Adolescence, loosely defined as the period between puberty and financial independence, now lasts about 15 years, twice as long as it did in the 1950s.

Part of this is due to the declining age of puberty in both males and females, but most of that extension appears in the 20s, when an increasing number of young people are still dependent on their parents. There is some concern that all of this dependence could lead to a lasting immaturity and failure to take on responsibility.

But according to developmental researchers, there is one lasting gift that extended adolescence can bestow, and it resides in the brain. “Neurobiological capital” is built through a protracted period of learning capacity in the brain, and it is a privilege that comes to those lucky enough to enjoy intellectually stimulating environments in late adolescence. Far from a contributor to emotional immaturity, the trend toward an adolescence that extends into the mid-20s is an opportunity to create a lifelong brain-based advantage.

Choirmasters’ records show that whereas choristers’ voices broke around age 18 in the mid-1700s, that age declined to 13 in 1960, and voices now break on average at age 10-and-a-half. Meanwhile, the age of first menstruation in girls has been declining by more than three months per decade. Much of that change comes down to improved nutrition, but in recent years the age drop has become a health concern. Marriage and financial security, on the other side of adolescence, now arrive close to age 30, in contrast to the early-20s marriages of the 1950s. In combination, those changes make for a more dominant life stage between childhood and adulthood.

Biologically, adolescence serves to prepare the brain for independence, and it represents the last surge of plasticity, when the brain is far more open to change than it was in middle childhood. The child-development expert Stuart Shanker says this pushes the teenager out of the house, replacing the overly comfortable embrace of the parent with the riskier world of peers and autonomy.

“Here, nature has spent eight or nine years getting the brain into a stable state in terms of higher functions, and then it’s all suddenly thrown back into chaos,” says Shanker. “We see changes in their reward system, which drives them into peer activities.”

The central task of adolescence is to develop the ability to self-regulate—to manage stress so that it does not interfere with the ability to follow through on plans and delay gratification. In particular, connectivity develops between the prefrontal cortex, crucial for executive functions like attention and decision-making, and the limbic system that drives emotion and reward.

Adults vary widely in the degree of success they achieve with this type of impulse control, and it has a large bearing on their life outcomes in work and relationships. Depression, obesity, and substance abuse are all exacerbated by self-regulation deficiencies, and adolescents who miss the opportunity to develop these capacities disproportionately run afoul of the law. For a teenager, potential rewards are almost irresistibly appealing, and the attendant risks seem worth it. The tendency to bet on a low-probability outcome is highest at age 16, and arrests peak at 18.

It’s not a matter of logic. In fact, a 15-year-old can reason and problem-solve as well as an adult in many areas of calculation, and they can accurately identify the risks of drug taking, unsafe sex, and crime. It’s when incentives, fatigue, social pressures, or stress come into play that an adolescent becomes more susceptible to irrational thinking. Last to develop are the circuits that deal with navigating other people’s needs and emotions, pushing past failure without losing determination, and connecting immediate actions to long-term consequences. With a longer adolescence, some people have an extra chance to strengthen these human capacities.

“There is reason to believe that continued exposure to novelty keeps the brain plastic for longer,” says Laurence Steinberg, a psychologist at Temple University whom many consider the leading expert on adolescence. Some of this evidence comes from brain studies of those who have had access to higher education.

The window for developing self-regulation closes when adult life settles into a routine, and the brain begins to exchange growth for efficiency. But if an adolescent continues to be stimulated intellectually—through higher education or travel, for example—their brain remains in its formative stage into the mid-20s, and even primes itself for future learning in adulthood. Dubbed “metaplasticity,” changing brain circuits through learning during adolescence can make subsequent modifications easier in those areas.

For parents, there are ways to encourage the brain to achieve better impulse control and stress management while the window of plasticity is open. Adolescents who develop exceptional self-regulation tend to have the benefit of parents who are neither too permissive nor too authoritarian. A warm, supportive, and firm hand lends teens the confidence to challenge themselves while steering them away from risky activities.

Steinberg likens the distinction between the brain’s adult state and its adolescent development mode to the difference between reading a new book and learning to read in the first place. For an adult to learn, she must pay attention and place information in the context of what she already knows. In contrast, an adolescent brain remembers things even through passive exposure. After that sensitive period has closed, the brain begins to focus on stabilizing the connections it has already made, through the process of myelination. It becomes exponentially more difficult to shape decision-making and higher cognitive functions. Those final pre-adult years may be the last, best chance to put a person on a healthy path.

While exciting as a prospect, the lifelong advantages of an extended adolescence can be economically exclusive. Protracted brain plasticity often depends on access to a stimulating environment—and the money that entails. Instead of falling into the rote tasks of an entry-level position after college, a debt-free graduate might volunteer overseas for a year and learn a new language and culture. In the world of enriching experiences and brain plasticity, as everywhere else, time is money. Parents who expect their children to make their way in the world after college, as they themselves did in the 70s and 80s, may be surprised to find they are not quite as obsolete as they had planned to be.

“Parents should prepare themselves for the timetable being different,” says Steinberg. “I never anticipated that my son would depend on us after college. Had I known that, we might have saved extra.”

To maximize neurobiological capital, it soon may not be enough for parents to sock away money in college savings accounts. Some may need to budget for a Neurobiological Runway Fund to cover the post-college years, too.