Miller v. Alabama

Adolescents have a diminished capacity for self-regulation and impulse control relative to adults; the neural systems supporting cognitive control and behavioral inhibition mature gradually across adolescence and do not reach adult levels until the late teens to early twenties.

Adolescents are more susceptible than adults to peer influence and to external pressure or coercion, with susceptibility greatest in mid-adolescence; the mere presence of peers measurably increases adolescents' risk-taking and shifts their decisions toward immediate rewards.

Adolescent personality and character are still forming and are not reliable indicators of fixed adult character; most adolescents who engage in antisocial behavior, including serious offending, desist as they mature, so adolescent conduct is a poor predictor of irretrievable depravity.

Adolescents weigh risks and rewards differently from adults: a reward-sensitive socio-emotional system matures earlier than the cognitive-control system, producing heightened reward-seeking, a weaker orientation to the future, and steeper discounting of delayed consequences during adolescence.

At the population level, childhood adversity -- adverse childhood experiences (ACEs) such as abuse, neglect, and household dysfunction, and a harmful family or home environment -- is associated with an elevated risk of adolescent antisocial and delinquent conduct, in a graded, dose-response pattern (more cumulative adversity, higher average risk).

The structural maturation of the human brain -- including cortical gray-matter thinning and continued development of white-matter connectivity in regions that support cognitive control -- continues throughout adolescence and into the early-to-mid twenties, later than the maturation of many other organ systems.