The social and historical contexts may influence the speed of development. In seven large, nationally representative surveys of U.S. adolescents 1976–2016 (N = 8.44 million, ages 13–19), fewer adolescents in recent years engaged in adult activities such as having sex, dating, drinking alcohol, working for pay, going out without their parents, and driving, suggesting a slow life strategy. Adult activities were less common when median income, life expectancy, college enrollment, and age at first birth were higher and family size and pathogen prevalence were lower, consistent with life history theory. The trends are unlikely to be due to homework and extracurricular time, which stayed steady or declined, and may or may not be linked to increased Internet use.