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In a new article published in Law and Human Behavior, Grace Icenogle and colleagues explore the question: When are adolescents mature enough to consent to a medical procedure, drive a car, drink alcohol, or be eligible for the death penalty?

In the United States, youth are legal adults at 18. Yet minors under 18 are permitted to make certain medical decisions for themselves or obtain a driver's license, while adults are prohibited from purchasing alcohol until age 21.

That said, age boundaries are in flux, and courts and policy makers are looking to developmental science for guidance on where to reset them. Indeed, citing developmental science, the U.S. Supreme Court has ruled that it is unconstitutional to sentence minors under 18 to death (Roper v. Simmons, 2005) or to mandatory life without parole (Miller v. Alabama, 2012).

Different legal matters require different capacities. For instance, making a decision about your health care necessitates deliberation, but resisting the urge to run a yellow light calls for impulse control.

Icenogle and colleagues argue that the facets of psychological development relevant to these two situations develop along different timelines.

First, cognitive functioning, including the ability to deliberate and reason logically, reaches adult levels by around 15–16. This ability is particularly important for deciding, for example, whether to undergo a medical procedure, or consider who to vote for.

Second, psychosocial maturity, the ability to exercise self-control even in emotional situations, does not become adult-like until later, sometime in the 20s. This ability is important for exercising good judgment when considering whether to hold a young person to adult standards of criminal responsibility and permit them to purchase alcohol.

The authors note that most of the relevant developmental research has been conducted in the U.S., but to the extent that policy makers look to science for guidance, it is essential to know whether these age patterns are mirrored in other geographical and cultural contexts.

To explore whether conclusions about maturity based on U.S. samples are generalizable, the authors examined the age patterns of cognitive capacity and psychosocial maturity using a cross-national studying comprising more than 5,000 participants between 10–30 years from 11 countries: China, Colombia, Cyprus, India, Italy, Jordan, Kenya, the Philippines, Sweden, Thailand, and the U.S.

Results indicate that cognitive capacity in most countries reached adult levels in mid-adolescence, while psychosocial maturity in most countries did not reach adult levels until the 20s. Although there were some deviations from these patterns, the authors suggest that age trends observed in the U.S. are replicated in this cross-national sample.

Ultimately, these findings are consistent with the premise that youth are mature in some ways before they are mature in others. Put differently, young people may be mature enough to make decisions in the doctor's office, which requires deliberation and logical reasoning, long before they are mature enough to exercise good judgment when drinking with their friends, which requires self-regulation.

Therefore, using two (or more) legal age boundaries is consistent with the developmental science.

Citation

• Icenogle, G., Steinberg, L., Duell, N., Chein, J., Chang, L., Chaudhary, N.,...Bacchini, D. (2019). Adolescents' cognitive capacity reaches adult levels prior to their psychosocial maturity: Evidence for a "maturity gap" in a multinational, cross-sectional sample. Law and Human Behavior, 43(1), 69–85. http://dx.doi.org/10.1037/lhb0000315

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Note: This article is in the Forensic Psychology topic area. View more articles in the Forensic Psychology topic area.