I would say if still youth then let him develop but don't let him have a hard training scedule, you don't want him injured at this time.
When he signs a proffesional contract, either loan him out if you know your never going to use him but make sure they say first team and have the recall clause there if he can't get first team.
If he's good enough for first team then give him appearances from substitutions often, if he's world class then he's good enough from 19-20 to become first team but if he's average let him stay until 22-23 and decide whether to sell him.