According to a report prepared for the U.S. Department of Health and Human Services,
The younger the age of first sexual intercourse, the greater the risk of unwanted pregnancy and sexually transmitted infections. This is because those who begin having sex at young ages are generally exposed to risk for a longer time, are less likely to use contraception, generally have more sexual partners, and tend to engage in higher risk sexual behaviors such as alcohol or drug use prior to sexual intercourse and having multiple concurrent sexual partners. It must be recognized as well that early intercourse is frequently not voluntary.
Less than 20% of teens become sexually active at 14 years of age or younger; however, if they do, they are six times more likely than their peers that self-identify as a virgin to drink alcohol once a week or more, four times more likely to have smoked marijuana and three times more likely to be regular smokers of cigarettes. Other research also shows that risk behaviors often appear in clusters. If an adolescent is engaging in one risk behavior then there is a strong chance there may be others. For example, many teens are either using drugs or alcohol when they first have sexual intercourse. Students seventh and eighth grade who use drugs and alcohol were more likely than non users to begin having sex.
A survey by the National Campaign to Prevent Teen Pregnancy found that "7% of youth used alcohol the first time they had sex, and 6% used alcohol the most recent time they had sex."
Researchers have also found that the younger an adolescent is at the time of their sexual debut, the greater the likelihood that they will engage in delinquent acts later. Adolescents who experience late sexual debut are the least likely to participate in delinquency. According to one of the study's co-authors, Dana Haynie, adolescents who start having sex at a young age may not be prepared to deal with the emotional, social and behavioral consequences of their actions. Study coauthor Stacy Armour theorized that adolescents "who waited longer than average may be developing friendships and relationships that can help protect them from potentially troublesome behaviors as they become young adults...The timing of events such as sexual activity can have profound consequences for adolescents, particularly when they occur prematurely...The timing of sexual initiation does matter. Adolescents need to be at a stage when they are developmentally prepared for it.