It didn't really bother me till my mid teens. I did try everything though. In the end lazyness and lager turned out to be the "fix". Once I left school there was no PE which meant no basketball (massive fan, played the weekends, lunchtimes and most nights). Fitness went out the window and nightclubs and drinking flew in. I noticed a massive change around 21 as before when I ate my weight in junk (sweets, biscuits, fizzy juice, crisps, every fat filled food you could imagine and no salad or veg) I wouldn't gain anything, whereas now I was properly gaining weight.
I started hitting the gym again and built up like I would have expected before (slower metabolism). I was quite happy but I changed out vodka drinks with pints of lager, ditched the gym after a couple of years and the rest is history