Neuroscience research since the late 1990s shows that the brain does not reach full maturity until about age 25, reports the National Center for Biotechnology Information. The brain's frontal lobes – home of executive functions such as planning, working memory and impulse control – are among the last to develop.
Traditionally, adulthood has been defined biologically as the end of puberty and legally as either 18 or 21 years old, with the underlying assumption that the brain has finished developing by that age. The National Center for Biotechnology Information explains that adolescent risk-taking behaviors, lack of impulse control and poor judgment can result from an immature pre-frontal cortex, as that is the seat of higher-order cognitive processes. This newer understanding of brain development means that policy makers, governments and social scientists are re-evaluating legal and societal expectations for young adults. Even so, science has not identified any direct correlation between actual behavior and specific stages of brain development.