Nick,
I was a 26 waist at16 years old and 115 lbs at 6"1" tall back then. My girth expanded to 27.5 and my weight to 130 Lbs in university. I stayed there until my 52nd birthday, then expanded to 36/37 waist and 190 Lbs. Now my goal is to get back down to between a 30 and 32. I hate the weight.
Pay attention to it while you are young and it easy to keep off, rather than a lot harder to take off at a later time.
Slainte