people can actually start receding at around your age. i started around sophomore year when I was 16.
and to answer your previous question: it most likely is male pattern baldness because of the fact that you just started noticing hair loss @ around the same time your body starts producing androgens, WHICH, incidentally, catalyzes follicular miniaturization in genetically susceptible individuals.
there's a chance it might not even be male pattern baldness; you might not even lose any more hair beyond that. but 9 times out of 10; male pattern baldness is the diagnosis for cases like this. Good news is that you caught it early enough to drastically slow it or even stop the recession--go to a derm to have it checked out and ask about minoxidil (idk if it is safe for minors to use, but considering that its OTC drug; i don't think its going to hurt you.