look to your mothers father for clues as to whats gonna happen to your hair. base your conclusions off of that. if hes 68 and still with flowing locks, you might not need to worry. if hes like mine, bald at 20, you might want to look into some proscar.
luckily, i dont seem to have taken it as hard as he did. but i did start thinning/balding at 17, exactly when he did.