this is not what he is asking. @Rev Dino
read again the question

No, age or experience (previous number of games) has no effect to the performance of a player.

but yes, the progress (gaining experience) of the younger usually is bigger than older players.
So it's a managerial matter and not coaching.
You must remember that it's not good to have an old 5* player to sell with a quality of 40 or 75 or 130.