To identify factors in adolescence that predict the onset of sexual violence in adolescence and young adulthood. Data were analyzed from six survey waves of the longitudinal Growing up with Media Study (2008-2018) conducted in the USA. Participants were 778 youth 13-18 years old at baseline, who completed online surveys assessing sexual violence behaviors and predictors. Sexual violence perpetration behaviors included sexual assault, rape, attempted rape, and coercive sex. Only 2% of females and 3% of males reported their first sexual violence perpetration by age 14. In contrast, by age 18, 6% of females and 12% of males had perpetrated their first sexual violence. For both males and females, the rate of the onset seems to plateau by age 22. Predictors of the onset of sexually violent behavior for those who began perpetrating when they were 14-17 years old were largely similar to those who began perpetrating when they were 18-25 years old. Alcohol plus other substance use, aggressive and delinquent behavior, caregiver monitoring, behavior problems at school, externalizing peers, exposure to community violence, and exposure to violent media were all implicated. Early prevention--well before college and perhaps even before high school--is needed to have an impact on the onset of sexual violence perpetration, as most perpetrators of sexual violence will have acted for the first time by age 23. Several modifiable risk factors observed in adolescence could signal the opportunity for targeted prevention to reduce the odds of onset of sexual violence.