USA - Brain

USA - Does the “minor age” really end at 18?

March 13, 2025:

March 13, 2025 - USA. Does the “minor age” really end at 18?

What Experts are Saying About Emerging Adult Behavioral Development Since Roper v. Simmons

Thirty years ago this month, the Supreme Court in its landmark decision Roper v. Simmons found capital punishment for individuals under 18 years of age unconstitutional under the Eighth and Fourteenth Amendments. In explaining their decision, the Court drew in part on “scientific and sociological” studies showing that a lack of maturity in youth can lead to “impetuous and ill-considered actions and decisions,” which supported the idea that this cohort were less culpable and therefore should not be subject to the death penalty.

The Court in Roper confined its ruling to 16- and 17-years (it had previously found that youth under the age of 16 were not death eligible), but extensive research now suggests that there is little difference between the developmental challenges that face adolescents (those under the age of 18) and those facing emerging adults (defined here as 18‑, 19- and 20-year olds) when it comes to impulse control, risk-taking, and the tendency to bend to peer pressure. Here, we share a taste of the research on emerging adult development, which presents a question similar to that addressed by the Supreme Court in Roper, that is, if the emerging adult cohort of 18‑, 19‑, and 20-year olds, whose actions are often both “impetuous” and “ill-considered” are actually mature enough to be considered culpable to the degree that would justify their exposure to capital punishment?

Changes in impulsivity and sensation-seeking are present through emerging adulthood, which could explain differences in risk-taking behaviors between this age group and adults. A 2011 study by Dr. Paige Harden & Elliot Tucker-Drob examined levels of impulsivity and sensation-seeking from the beginning of adolescence through emerging adulthood. The study involved a large sample of 7,640 individuals, between the ages of 12 and 24, who self-reported on survey measures of impulsivity and sensation-seeking, both traits influencing risk-taking behaviors. Regarding impulsivity, the study found that it declined with age until leveling off in the mid-20s, which could be explained by neuroscience research that has shown the gradual maturation of impulse control areas (i.e. the cognitive-control system) through emerging adulthood into an individual’s mid-20s. Regarding sensation-seeking, the study found it to increase, until peaking around age 16, thereafter very slowly declining through emerging adulthood and beyond to the mid-20s. The trend in sensation-seeking could be explained by neuroscience research that has shown brain regions responsible for emotions, novelty, and reward (i.e. the socioemotional system) are more susceptible during adolescence and emerging adulthood when compared to both children and adults. According to the authors, this is the first longitudinal survey data study to support neuroscience findings of a dual-system model of adolescent development comprised of the sensitive socioemotional system and the still-maturing cognitive-control system.

In emotional contexts, emerging adults, like adolescents, are more likely to have issues with self-control and decision-making. A 2016 study by Dr. Alexandra Cohen and colleagues compared the cognitive control, including decision-making and impulse control, of three age groups (age 13 – 17, age 18 – 21, and age 22 – 25) during emotionally-arousing and non-arousing conditions. Relative to adults, both teens and emerging adults demonstrated diminished cognitive performance when presented with negative cues (i.e. images of fearful faces). However, emerging adults did not differ from adults in the non-arousing condition. This suggests that the cognitive control of emerging adults is vulnerable to negative emotional influences and marked by continued development of the prefrontal circuitry. So, in emotional situations, that is situations that require quick-decision-making, or “hot cognition,” emerging adults may perform poorly when compared to adults. By way of contrast, in non-emotional situations that allow for thoughtful, deliberate decision-making, emerging adults may perform similarly to adults.

Emerging adults, like adolescents, are more likely to engage in risk-taking behavior when surrounded by peers. Studies support the idea that emerging adults are prone to taking greater risks when in a group of same-aged peers. A 2005 study by Dr. Margo Gardner and Laurence Steinberg looked at 306 individuals in three age groups: adolescents (13 – 16), youths (18 – 22), and adults (24 and older), to assess the effect of peer influence on risk-taking behavior. The study found that while the whole sample engaged in more risk-taking and risky decision-making, middle and late adolescents (from 13 to 22 years old) were more susceptible to this peer influence in comparison with adults 24 and older. In one case identified by DPI, five youth were sentenced to death in Texas for a group rape/murder of two teenage girls as part of a gang initiation. Peter Cantu, Jose Medellin, and Sean Derrick O’Brien were all 18 at the time of the crime and all three were executed. The two remaining members of the group, Raul Villareal and Efrain Perez, had their sentences commuted because they were underage.

Sources

Cohen, A. O., Breiner, K., Steinberg, L., Bonnie, R. J., Scott, E. S., Taylor-Thompson, K., Rudolph, M. D., Chein, J., Richeson, J. A., Heller, A. S., Silverman, M. R., Dellarco, D. V., Fair, D. A., Galván, A., & Casey, B. J. (2016). When Is an Adolescent an Adult? Assessing Cognitive Control in Emotional and Nonemotional Contexts. Psychological Science, 27(4), 549 – 562. https://doi.org/10.1177/0956797615627625

Gardner, M., & Steinberg, L. (2005). Peer Influence on Risk Taking, Risk Preference, and Risky Decision Making in Adolescence and Adulthood: An Experimental Study. Developmental Psychology, 41(4), 625 – 635. https://psycnet.apa.org/doiLanding?doi=10.1037%2F0012-1649.41.4.625

Harden, K. P., & Tucker-Drob, E. M. (2011). Individual differences in the development of sensation seeking and impulsivity during adolescence: Further evidence for a dual systems model. Developmental Psychology, 47(3), 739 – 746. https://psycnet.apa.org/doiLanding?doi=10.1037%2Fa0023279

https://deathpenaltyinfo.org/news/articles-of-interest-what-experts-are-saying-about-emerging-adult-behavioral-development-since-roper-v-simmons