Well, mine started receding up front a little at about 23 and at about 28 the "solar panel" on the top back started appearing. 29 now and hasn't progressed much further. I cheat though. I have hair about half way down my back so what grows out on top (in front of the bald spot) pretty much covers the thinning area.
If it gets real noticeable I'll probably just do the shaved "peach fuzz" look. Guess I'm lucky though 'cause my mom tells me my grandpa was TOTALLY bald on top by the time he turned 19!
Way I see it, I lasted 10 years longer already!