FIGURE 10.2 Many Virgins For 30 years, the Youth Risk Behavior Survey has asked high school students from all over the United States dozens of confidential questions about their behavior. As you can see, about one-third of all students have already had sex by the ninth grade, and about one-third have not yet had sex by their senior year—a group whose ranks have been increasing. Other research finds that sexual behaviors are influenced by peers, with some groups sexually experienced by age 14 and others still virgins at age 18.