I'm 24. I lost my virginity at 23 to a woman who turned out to be essentially a w**re. If and when I do get married, I won't have that left to give to my wife. Which, hey, not much I can do about it now, but...every time I think about that woman, I wish I'd been smart enough to wait. No, there's no kid and no medical issues involved. But that was a mistake that can't be undone.
Remaining a virgin until marriage isn't old-fashioned. It shows you have the self-restraint to hold off until you meet the person you want to spend the rest of your life with. And it shows that you care enough about your future partner to be patient and share that most private aspect of your life with them and them alone.
I'll always regret my decision. I learned some hard lessons, but I'd always planned on abstaining until marriage. And once you take that step, there's no going back.