The rest is basic economics.

When I was a teenager, I don't remember a huge distinction between the people who where having sex, and the people who were having oral sex. One eventually led to the other. No one I knew was getting into either when they were twelve.

"When the price of Coca-Cola rises, rational cola-lovers drink more Pepsi. When the price of penetrative sex rises, rational teenagers seek substitutes. Perhaps we shouldn't be surprised that even as the oral-sex epidemic rages, the Centers for Disease Control and Prevention reports that the percentage of teenage virgins has risen by more than 15 percent since the beginning of the 1990s. Those who are still having sex have switched to using birth-control methods that will also protect them from sexually transmitted infections. Use of the contraceptive pill is down by nearly a fifth, but use of condoms is up by more than a third. The oral-sex epidemic is a rational response to a rise in the price of the alternative."

Full article at http://www.slate.com/id/2148583/nav/tap2/