This is a split topic with me. I am not innocent, but I do believe that a person should wait until marriage. I have much more respect for a person that remains a virgin until then.
You know that it is never too late with G-d. You can save yourself from this point forward.
I've heard of people who have had sex deciding to have a second virginity where they decide from this point forward to save themselves for marriage. It's not really being a virgin again, but it is making a commitment to a moral way of life and doing the right thing in G-d's eyes.
If you allow me, I can tell you about my personal experience.
WHen i was only a few years younger than Yaacov, I had the same idealism of waiting till marraige. And I think I probably would have been able to pull it off until I thought I met the girl of my dreams. We couldn't wait. Marraige was out of the question for us. We were both still in school. Niether of us had really ever dated many other before us. We did it. Thank Gd, it didn't work out for us. But a pandora box opened and now I knew what it felt like.
Today, whether I were dating a virgin or not, it would be between me and her what we decide to do before marraige. But the reality is, it's much much much much better even if in love, to wait till that Ketubah is signed and the marraige is consumated. And for me, it's really really really really really hard to not do it being in love with someone and knowing what it feels like already to do it.
However, there is a conflict with doing it to get it out of the system versus waiting completeley. In the first relationship, I had nothing out of my system. I was with a really nice girl, but she wasn't perfect for me. She and her family had major flaws, but I was too innocent and blind to notice them. If it had gotten to the point that we got married after several years of dating, I can assure all of you, there would be potential for divorce or a very unhappy marriage. Maturity was an issue, but it was also the desire to go out there and see what's out there. Luckily I have had the opportunity to date a lot since.
Now, today, I have the experience, I have the knowledge, I'm much more mature. I know what I want. And now that I do know what I want and have experience, it's good for a woman who wants to be with a man who has it out of his system and has knowledge and experience on what to do in bed. Some women, especially the ones who are still virgins until marraige, want to be with a man that knows what to do. They don't want the "blind to lead the blind".
I"m not saying that guys should now just go out and have sex before marraige. In fact, a couple can figure things out on their own and share the hottest sex imaginable as they grow older and wiser.
So anyway, my point is that i agree wtih CF and Bullcat and any parent with young kids and teenagers... Please encourage them to wait till they get married. Don't let peer pressure get to them. Make sure they fall in love with the right person...not just with anyone of the opposite sex. The right person with the right family. Better that if they are virgins at that time they are with someone who can hold back until the marraige is consumated. And better if he is able to provide for a home for his family than be still in school living in a tiny dorm room. In modern times, it's not easy to have all that all at once.
That's the only thing I disagree wtih with CF.
In reality, however, I would want a study to be done on the success of marraiges with those who had premarital sex either with their future spouses or multiple partners before they got married versus those who stayed virgins, and see if there is statistic significance.