Researchers at San Diego State University and Bryn Mawr College analyzed seven large surveys of 8.3 million 13 to 19-year-olds between 1976 and 2016.
The results of the study have been published in the journal Child Development.
"The developmental trajectory of adolescence has slowed, with teens growing up more slowly than they used to," lead author Jean M. Twenge said.
Teens are also leaving it longer to take up adult responsibilities such as driving and working.
"In terms of adult activities, 18 year olds now look like 15-year-olds once did," Twenge added.
The research team says the surveys were nationally representative, reflecting the population of US teens in terms of gender, race/ethnicity, socio-economic status, and geographic region.
Each teen was asked how they spent their time and how often they took part in adult activities such as drinking alcohol, working, driving, dating and having sex.
According to the study, the decline may be linked to the substantial increase in time teens spend online. The report dismissed homework and extracurricular activities as contributing factors.
Comment: The report sounds like its missing some crucial factors!:
- Less work, more video games: The state of young men in America
- Survey says NYC teens are too busy playing video games to smoke cigarettes or have sex
- Research confirms links between violent video games and increased aggression, decreased prosocial behavior
- Video games 'can alter children's brains'
The paper noted the importance of social and historical contexts in influencing the speed of development, explaining that certain cultures promote a 'slow life' strategy while others embrace a fast lifestyle involving adult activities during adolescence.
It said teens were less likely to engage in adult behavior when families had fewer children, a higher median income, and during periods of time when fewer people died of communicable diseases.
"Our study suggests that teens today are taking longer to embrace both adult responsibilities (such as driving and working) and adult pleasures (such as sex and alcohol)," co-author of study Heejung Park said.
"These trends are neither good nor bad, but reflect the current US cultural climate."
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