Sex before marriage?

I was having an argument with a friend about sex and what is the appropriate age to have it at.
This friend, who was telling me that sex should be had before marriage, was saying how we'd be so crap at it when we grow up and get married, if that's the only time we plan on doing it.
Then he went on to say, all of a sudden, that sex is a wonderful thing, and how that two people who really, really love each other don't care what each other looks like. They care for only one thing, and that is their love.

So then I asked myself, so if sex is truly such a wonderful display of love to each other, why must we be good at it?
If two people genuinely love each other, with real love, not passionate lusty movie-like love, then they wouldn't be bothered if both of them were complete bollocks at sex. They wouldn't care one bit.

It's a mystery, that's what sex is.