if a player is of outstanding quality then ehs good enough no matter how old he is imo
but as a rule, lets say you acquire the player aged 167/17. i would stick him in your u18s and also make him available for reserves. start him in league cup games and also some fa cup against much poorer sides. use him from the bench in a handful of league games, especially off the back of a good performance for the reserves.
next season, same again, but only in the reserves, no youth football. play him in more league games.
next season is a difficult one. its either loan time if you think hes developed enough, or stick to last seasons schedule with a bit more game time.
next season is either loan time again (or first loan if he stayed at the club in the previous season)
if he impresses on loan then the time comes when you need to start playign him as a first team regular or he will stagnate
also, tutor him with an experienced pro who plays in his position