There's something in most sport called Relative Age Effect. Ie the kids born in the early part of the selection window progress as they are usually bigger and stronger, but not always better.
But being big and strong and fast means you get more ball time and more time to impress.
A lot of the top academies are looking to reduce the the RAE influence by bio bandning so they don't miss out on those who might be binned off for being too small.
Give the lad some time... Look at someone like Andy Murray, always getting cramp etc and being too skinny when he was young. Then turned in to a bit of a beast (hip notwithstanding!)