Regarding the question of whether abstinence-only sex education delays loss of virginity, I have the following to say. The education I received was abstinence-"plus", but it (particularly a very Christian guest speaker), in conjunction with the social environment I was brought up in - which taught that sex is naughty and only the bad kids engage in it outside of marriage or very committed relationships, or before reaching the age of 18 - was enough to prevent me from going "all the way" with my girlfriend when I first had the chance. I didn't get another chance until about ten years later, after which point I thought, why the hell did I wait so long to get started?
The point I wish to make is this: even if abstinence-whatever education does delay loss of virginity, the question I ask you is - why does it matter when people start having sex? Isn't it far more important that when people do have sex - no matter what age that is - it's an informed decision they've made willfully and consensually, and that they are knowledgeable enough not only to be able to practice safe sex, but also to understand why practicing safe sex is a damn good idea? That people are having safe, consensual sexual encounters in a pleasurable and psychologically positive context is far more important to me than whether or not they 'wait for marriage', or whether they start experimenting at 25 or 15 years of age!