Just stop playing your balls and start playing basket balls,
everday b4 each meal, jump 300 times, I can assure you that by 21
you will be at least 175.
That was what i am trained since 12 yo, my aunt was a former
taiwanese model, she taught me to skip rope and play net balls. I
have to do 300 skipping per day, 200 hula loop round my waist, jump
200 times before meal with sport bra on, (otherwise my boobs may
sag) and play net ball 3 times a week in school and also at my Dad
club.
It been going on till now, me stand at 176 only. weight 50kg, no
sickness, clean and sharp, house full of trophies from netball
games, longjump, highjump and triple jump.
So you try it out, you maybe a bit too old, but still have chance,
because you are a boy. Another thing is that you must have
determination and disciple, dun give up, most pple give up exercise
stuff very easily.