Wayne Rooney had a stellar career. Judging him in the twilight of his years isn't balanced. And if you believe his smoking and getting over weight was because he played when he was young then I'd disagree with that and put it more down to his upbringing, his personality, his friends and so on. But look let's put Wayne Rooney to one side. What about Ryan Giggs? Actually, let's bring it closer to home, what about David Silva? At 18 he was playing over 25 games per season out on loan. This is the fundamental point, players at that age need to play to develop.
Anyway the bigger question I raised was do people think Foden is developing at about the right pace, being held back or is actually being developed better than you expected. I believe he should have more minutes than he's had. And if he can't get it in the first team he should yo out on loan.