There are a number of studies out there regarding relationships with large age differences that have drawn some not-so-positive conclusions. According to studies by the Guttmacher Institute, women under 18 with older male romantic partners are more likely to engage in sexual activities and less likely to use contraception when doing so, putting them at greater risk for both STIs and pregnancies. We know that with “teen” pregnancies, more often than not, while the mother is a teen, the father is often an older teen or a legal adult. Today, about half of the births to teen mothers involve men ages 20-24, and an additional one-sixth are over age 25.
In 1999, a study about young women in the United States concluded that “[a]lthough the proportion of 15-17-year-old women who have a much older partner is small, these adolescents are of concern because of their low rate of contraceptive use and their relatively high rates of pregnancy and birth.” A recent study found that 6.7 percent of women aged 15-17 have partners six or more years older. The pregnancy rate for this group is 3.7 times as high as the rate for those whose partners are no more than two years older (Planned Parenthood 2004; Darroch et al., 1999) Another study in 2002 determined that “[y]oung adolescent females with substantially older partners are much more likely than their peers to have sex with their partner.”
ETR Associates also reminds us, via more data from AGI, that a substantial percentage of younger teens who have had sex have been forced. "Some 74% of women who had intercourse before age 14 and 60% of those who had sex before age 15 report having had sex involuntarily," as do 40% of those who had sex by 15, and 25% by 16 also reported, the Guttmacher Institute said. "Sex among young adolescents is often involuntary; it frequently involves a man who is substantially older than the woman, which may make it hard for the young woman to resist his approaches and even more difficult for her to insist that contraceptives be used to prevent STDs and pregnancy" (Alan Guttmacher Institute 1994, pp. 28, 73-74).