I read somewhere, can't remember, that it's better that you play and train with your biological age when your in your teens, as we all develop at a different rates.
I thought that this was something UK Rugby are looking into, as it allows good techniques to be learn't and not lost from being physically disadvantaged.
As at 15 i was 5ft4 but but six months later i ended up at 6ft6. So I would have completely missed any scouting as I would have been considered too small.