I'd have to say "To thine own self be true". If someone holds such strong religous or idealogical beliefs that waiting seems like the right thing, then maybe it's the right thing for them.
I think that making it all the way to your twenties until you marry is difficult, and while you're going through your sexual development, it can actually cause problems in the form a divergances from healthier sex drives, but that's the chance you take. Learning to substitue something else for sex, or learning to feel guilty about your sex drive will last a life time, I wish more people would consider that. There are a lot of fucked up adults who still have not figured out that sex is okay and your drives are natural. Ever hear of the madonna/whore complex? It's pretty horrible stuff.
Everyone's time frame is different, but personally, I'd NEVER commit to someone in a relationship without knowing if we were sexually compatible. Sex is a very important part of a love realtionship, and just like I wouldn't marry someone without knowing their philosophical views, their politics, religous opinions- I also wouldn't jump in blindly not knowing how they are about sex. Seems like common sense. There are literally MILLIONS of sexless marriages out there, would you want to risk that?