CezzaXV
I think with anything you're writing, you need to know enough about what you're talking about to write accurately about it, and that includes sex. Not being a virgin probably helps, but it is possible to still know loads about sex and be a virgin.
Probably helps? There's no probably about it.
razz But like Axioma said, even not being a virgin doesn't automatically mean you can write sex very well. A great deal of it is writing skill and imagination. Of course, depending on your libido, you can draw on and extrapolate from experience with masturbation to approximate what sex would be like, and while it won't always be entirely accurate, most people are not going to notice, since it's only the most intimate details (mainly the sensations of climax in/on, mouth and tongue on skin, etc.) that would be a little lacking. Even these details, though, can be fleshed out if you have a few friends who are tolerant enough of probing questions to give you that sort of information. (This is something I'm well blessed with, since one of my erotica projects is first person as a woman, but not being a woman, I'd be unable to effectively write certain elements of the story. A large portion of my women friends have been good enough to put up with some (sometimes) very probing questions so I could get that information in order to write the character more realistically.)