(CNN) The percentage of boys who start having sex at a young age can vary based on factors such as where they live and their mothers' education level, according to a new study. Yet among those boys, only about half described their first time as something they fully "wanted."

The study, published in the journal JAMA Pediatrics on Monday, found that 3.6% to 7.6% of boys and young men in the United States -- nearly 1 in 13 -- report having had sex for the first time before they turned age 13.

The researchers are calling for more education, care and conversations about supporting healthy sexual development in boys.

"Too often, the sexual health needs of young men are overlooked. These findings have major implications for the timing of sex education and sexual and reproductive health care," said Laura Lindberg, a principal research scientist at the Guttmacher Institute, a reproductive rights think tank, and first author of the study.

In general, about age 17 is when most boys and girls have sex for the first time -- but boys are more likely than girls to have sex for the first time before 13, according to data from the US Centers for Disease Control and Prevention

Data in the first system was collected in questionnaires completed by students in grades nine to 12 and involved 19,916 male students. The family growth survey data was collected through in-person interviews with 15- to 24-year-olds and involved 7,739 males.

The researchers analyzed that data with a close eye toward demographic factors, where the boys lived and how much respondents wanted that first experience to happen.

To measure "wantedness," the National Survey of Family Growth asked the respondents to describe how much they wanted the encounter to happen, choosing between "I really didn't want it to happen at the time," "I had mixed feelings -- part of me wanted it to happen at the time and part of me didn't" and "I really wanted it to happen at the time."

The researchers found that sex before 13 was reported by 7.6% of the male high school students in the Youth Risk Behavior Surveillance System data and 3.6% of the respondents in the National Survey of Family Growth data.

The National Survey of Family Growth data showed that among those who reported having sex before 13, 8.5% described it as "unwanted," 37% had mixed feelings about it, and 54.6% described it was "wanted." Most described their first sexual partner as a friend.

That was similar to findings among males who had sex later than 13, the study found, which was that 5.4% reported it as "unwanted," 31.3% had mixed feelings, and 63.3% described it as "wanted."

The Youth Risk Behavior Surveillance System data showed that, across 15 metropolitan areas in the United States, the percentage of male students reporting having sex before 13 varied widely: 5% in San Francisco to 25% in Memphis, Tennessee.

The researchers also found that respondents whose mothers had a college degree or higher educational level were less likely, by a statistically significant amount, to report having sex before 13, and reports of having sex before 13 were higher among black males.

The study had some limitations, including that the younger the survey respondent the more likely they were to report having sex before age 13, and the data focused only on male-female sexual intercourse, not other types of sexual experiences.

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They called for improvements in sex education and screening for sexual activity in youth.

"Any messaging, whether from clinicians or schools or parents, must recognize pressures that 'manhood is something that boys must make happen, by passing certain social milestones,' such as having sex. It is critical to engage young men in self-reflection about the real pressures US society places on them that affect their overall health and well-being," Bell and Garbers wrote.

"Any discussions associated with pressures should include topics of 'what it means to be a man' and soliciting and giving consent," they wrote. "With the support of caring adults, led by existing national guidelines that call for developmentally appropriate interventions early in life, boys can achieve healthier milestones without ambivalence or societal risk."