Eh, yeah, my hair started going at 18ish. I'm 23 now, and it's still not particularly noticeable unless I point it out. Of course, I had extremely thick hair to begin with.
Like you, I pretty much completely freaked out and did a shitton of research on the subject. For instance, I learned that something like 10-20 percent of men start losing their hair in their late teens/early 20's. That may not seem like much, but that's still 1 or 2 guys out of 10. So there's quite a few out there going through the same thing. I started taking Propecia soon after I realized what's happening, as it seems to be the only method of combatting hairloss that has been scientifically proven to have some beneficial effect (other than hair transplants, but that's a whole other set of problems). According to the research, it slows or halts hair loss on the crown of your head, but is less effective at dealing with your hairline. The research also shows that it may begin losing its efficacy after a number of years of taking it.
I no longer feel the intense anxiety and such concerning my hair loss that I once did. It has not impacted my life negatively in any way that I can see. Women still find me attractive. Confidence attracts women much more readily than hair. The attitude you want to go for is, "Yeah, I'm a balding badass, what of it?" In fact, I no longer really make any attempt to hide it. I'll bring it up in casual conversation if it seems pertinent.
And don't worry, as the years go on, more and more of your friends will
be going through the exact same thing. You're a trend setter
.
EDIT: A few additions, as I've had some time to think on the subject, and I'm drunk.
For one thing, once my hair started going, I developed a "bald-dar" (a derivative of gaydar) so to speak. You really start noticing how many other guys are going bald once you start to. And it's really surprising. For example, I realized that the homecoming king during my senior year of high school was going bald. Heath Ledger? Going bald. Lots of men are going bald. Many of them highly successful people.
The only way it can negatively affect your life is if you let it. For a couple of years I was anxiety-ridden that people would figure out that I was losing my hair and that somehow I'd become a loser or a failure. I started wearing hats constantly, doing all sorts of stupid shit. All of which just really pointed out what was happening, and that I was uncomfortable about it. Don't start wearing hats all the time, heh.
The truth is, your friends won't give a damn, besides possibly giving you a little shit, to which you give them shit in turn. And the only women who would care are most likely shallow creatures you don't need to be with to begin with. As I said, women are far more attracted to confidence than hair. I've actually been with more women since I've started losing my hair than before, as I gained more confidence in myself during that period.
Enough rambling. As for some practical advice: keep it short. It just looks horrible and sad when you grow it out long to try and compensate. It's actually easier to tell a person's going bald when their hair is long, as the thinning hair is typically lighter-colored and the thinning patches are more prominent. Keeping it short lets you keep a clean looking look where it is less obvious, and far less sad. Compare Andre Agassi just before he started shaving and now.
I'm also in much better physical shape now compared to how I was before I started losing my hair. I am much more motivated to keep in shape and looking good, and that has paid multiple dividends. Hitting the gym is never a bad idea. I may have lost an inch of hairline, but I've gained some abs and pecs. Not a bad tradeoff. The endorphins are nice too.
As for fighting it; as I said, Propecia has been proven to combat hair loss at the crown. Rogaine is said to help hairloss at the hairline, although the application of that oily muck was too much of a headache for me to deal with. You may feel differently. Overall, though, neither of these medicines have proven to be effective in the long run. Thus, the best idea is to learn to accept the hand that's been dealt you, and making the most of it. Which, for me, has been not bad at all.