Poor lad; comes to a rugby forum asking advice with no clear answer so far. That said and having no memory of what u16 rugby was like I have to say it is up in the air however. Best would be to just start somewhere and then move on as you get to know the game better and develop.
I started at lock because I was tall for my age, moved to no.8 and ended up on the wing because though I am tall and fast I was just too damn lazy to get stuck in and liked to have a run with ball in hand rather. Suited me just fine hanging back fielding kicks and then running it back or chasing kicks and blindsiding the catchers (I can't remember recieving the ball much from my centers LOL). You'll find what you like and what you're good at along the way and many skills you learn in one position come in handy in another and might just set you apart at your level.