Depends I think on how old they are. If they're pretty young, then it's more normal to want to hold on to their virginity. If they're older though, it could be a sign that something else is going on. My ex was the exact same way, hold onto it until marriage, religious. But she also just turned 30, and unfortunately there was alot of other stuff that I actually didn't see about her until later (and more importantly, how she used others for what they could do for her) Not full blown use, but use like a child. Judgemental. No sense of empathy either with her, such as getting her 75 year old dad to do wallpainting and moving for her. Just my example though. Also was semi-abusive towards animals.
My advice, look very carefully at how she interacts with others. At all times. And don't expect anything really sexual. We did some stuff, and then I pushed it too far, I guess.
Actually PlayHer Man, that's exactly what my mom thinks my ex is as well (closet lezbo). Could be right.