While it's possible that as many as one in 13 boys in the US have sex before reaching their teens, the chance that they will do this varies widely depending on where they live, a study suggests.
Researchers examined data from two nationwide surveys - one with almost 20,000 male high school students and another with more than 7,700 males ages 15 to 24. Overall, 7.6 per cent of high school students in the first survey and 3.6 per cent of participants in the second survey reported having sex for the first time before age 13.
Across cities nationwide, the proportion of boys who reported having sex before age 13 ranged from as small as one in 20 in San Francisco to as large as one in four in Memphis, Tennessee.
"Adolescent males' attitudes and value about their sexuality and masculinity are influenced by the social context of their community," said lead study author Laura Lindberg, a researcher at the Guttmacher Institute in New York City.
"Our findings reflect that where you live exposes you to different social norms about manhood," Lindberg said by email. "The variation across settings means that programs for young people's development and health need to be tailored and responsive to the communities they are in."
In most cities examined in the study, black males were more likely to report having sex before age 13 than their white counterparts. In many cities, Hispanic males were also more likely to have sex at young ages than white boys.
Compared to black males, white males were 79 per cent less likely to have sex before age 13, and Hispanic males were 73 per cent less likely.
In the survey of older teens and young adults, 8.5 per cent of participants who had sex before age 13 described it as "unwanted," and another 37 per cent said they had "mixed feelings" about it. A similar proportion of young men who waited longer to have sex described their first encounter as unwanted or had mixed feelings.
The two surveys asked about sex differently. The larger one asked high school boys about the age of first sexual intercourse without specifying the partner's sex. But the smaller survey, involving males from adolescence through early adulthood, asked about the timing of first heterosexual intercourse.
Another limitation of the analysis is that it focused on vaginal-penile intercourse, which may not necessarily be the type of sexual encounter all young people have or want to have, the study authors note in JAMA Pediatrics.
"Of course, young people engage in a range of sexual behaviors, and age at first vaginal sex is only one indicator of sexuality," Lindberg said.
Still, the results suggest that parents and educators may need to start talking with children about sex at younger ages if they want to ensure kids have all the facts about safe sex and relationships before they become sexually active, the study team notes.
"From naming body parts to explaining where babies come from, parents should be talking early and often with their children in an honest way about sex," Lindberg said. "Parents and educators can't wait until a high school class to cover key topics when many young males start having sex before this."