You're right, but at your age it's really hard to determine - and I have alot of friends with the same 'problem', friends who can't put on weight and some eat non stop - that's because of their metabolism or that they just have small frames but it doesn't always stay that way, a couple of them did put on quite a lot of weight in the last couple of years and they are about 22 now. They never thought they would but they did and I think it's because it all just caught up with them - so whatever happens it's best just to try and accept yourself for who you are I think and just try to be as healthy as possible. I'm sorry if that doesn't help or make you feel any better 馃檨 but I seriously think it's too early to really tell in general.