Setting the Stage--Adolescence
The limitations of the "teen brain" has been well publicized in the mass media, helping parents, teachers, and others understand why it may be difficult for teens to meet our expectations and demands for managing emotions, handling risks, responding to relationships, and engaging in complex school work or employment. In early- and mid-adolescence, the brain undergoes considerable growth and pruning, moving generally from back to front areas of the cerebral cortex.
Changes in Young Adulthood
At the same time that young adults are experiencing new levels of sophistication in thinking and emotional regulation, their brains are undergoing changes in precisely the areas associated with these functions. While it is not possible to determine cause-and-effect, brain and behavior are changing in parallel.
20s and beyond
According to recent findings, the human brain does not reach full maturity until at least the mid-20s. (See J. Giedd in References.) The specific changes that follow young adulthood are not yet well studied, but it is known that they involve increased myelination and continued adding and pruning of neurons. As a number of researchers have put it, "the rental car companies have it right." The brain isn't fully mature at 16, when we are allowed to drive, or at 18, when we are allowed to vote, or at 21, when we are allowed to drink, but closer to 25, when we are allowed to rent a car.