Same story here - started noticing thinning of my hair at age 21, got on propecia at 23. I did experience a drop in my sex drive, so I got rid of the propecia. However, I was worried as hell about sexual side effects from the beginning on, so there's a good chance that at least part of the problem was due to the placebo effect. When I stopped taking propecia, my sex drive went back to normal fairly quickly.
I'm almost 26 now, and although I'm far from bald, the "horseshoe" pattern is coming through. Although I'd like to have a full head of hair with a nice cut, I've come to accept that it just ain't gonna happen. Every week I clip my hair down to 1/8", and it's a look I can live with just fine. (It's almost funny - in high school I shaved my head, even though I could have grown any hair I wanted...)
I'm not trying to tell you not to fight against it and accept yourself the way you're meant to look, or some similar zen shit that everybody loves to tell people who get screwed by genetics. You're young, and you wanna look young, so by all means fight for your hair - it could work. I just wanna let you know that at some point, you will be used to the fact that you have hair loss - sooner or later. When you're going for a mature look instead of a young guy look, full hair is definitly not a necessity. If you take care of the "other stuff" (read: stay fit and wash yourself), your appearance will primarily come down to your charisma and confidence.
Until then, good luck! You might also wanna look into supplementing with zinc, and using shampoo with caffeine in it - maybe it works.