Male Baldness Info

so heres the situation, i am 17 and i am starting to notice that the hair on the crown of my head is starting to become thinner, revealing my scalp.
i know this cant be male pattern baldness because everyone in my family (moms and dads side) havent started showing signs of male pattern baldnesss well into ther 40s and when they do start to thin, they thin in the front.
what can this be?
is it because i weightlift four times a week?
does weightlifting speed up the male pattern baldness process?
thanx in advance