Teenagers in America today are about three years behind their counterparts from the 1970s when it comes to taking up sex, drinking alcohol and working for pay, researchers said Tuesday. The findings in the journal Child Development were based on an analysis of seven large, nationally representative surveys of 8.3 million teenagers between 1976 and 2016. The surveys sought to find out how those aged 13 to 19 spent their time, and how often they engaged in adult activities such as drinking alcohol, dating, taking jobs, driving, or having sex, said the report. What researchers found was a "broad-based cultural shift," said the study. Adolescents in the 2010s "are less likely to work for pay, drive, date, drink alcohol, go out without their parents, and have sex than adolescents in previous decades," it said. These changes were apparent across the nation, and regardless of race, gender or socioeconomic lines. "The developmental trajectory of adolescence has slowed, with teens growing up more slowly than they used to," said lead author Jean Twenge, professor of psychology at San Diego State University. "In terms of adult activities, 18-year-olds now look like 15-year-olds once did."   - More time online -   Researchers suggested that spending more time online -- a habit that has increased "markedly" -- could be a leading factor in the shift. While some have suggested that more homework or extracurricular activities are turning teens' attention away from adult behaviors, the study found that was not the case.  "Time doing those activities decreased among eighth and tenth graders (age 13-16) and was steady among twelfth graders (age 18) and college students," it said. Whatever the reason, researchers said it appears teenagers today are slower to embrace both the risks and responsibilities of adulthood. "This large new study certainly seems to contradict the common wisdom that children are forced to grow up earlier and earlier in our increasingly complex society," said Michael Grosso, chair of pediatrics and chief medical officer at Huntington Hospital in New York. "Of course, population-based trends can obscure the fact that for many individuals and groups the story may be different," added Grosso, who was not involved in the research.  According to pediatrician Victor Fornari, there can be an upside to this trend. "If we can delay alcohol consumption and entry into adult intimacy it is generally a good thing," said Fornari, director of child and adolescent psychiatry at Zucker Hillside Hospital in Glen Oaks, New York. "Hopefully it will result in less adolescent alcohol problems and fewer unwanted pregnancies and sexually transmitted diseases," he told AFP. But the increasing amount of time children spend online is also a concern, he said. "This is not normal that people are spending hours on various social media sites," said Fornari, who was not involved in the study. "The real issue is going to be in the next 10-15 years. What will we learn about those adolescents who entered the computer age with their parents' iPhone when they were one, and have been looking at YouTube videos to keep themselves soothed since before they were two?" He urged parents to limit their children's screen time and get them outdoors, discovering books, and playing with others. "We want our kids to be engaged with physical activities, reading and not spending as much time on devices," he said.