Xavi had played about ten senior games by the time he was the same age as Gilmour is now. People seem to think Football Manager = real life and you're a busted flush if you're not pushing 100 appearances by 21.
We only need him to be better than Kenny McLean and Callum McGregor to improve our first team, and he already is. He will improve with a full season playing for a weaker team in a strong league, and then he will be at Chelsea or a level not too far off that the following season. If we're hoping for him to be a world class option or close, he's well on the right track.