I'm not talking I want to become back for old player's stats to be like when they young instantly. I want to ask growth shape after I change player's age.

when I change players age, they keep grow up like young players? and don't decline stats even they have been old player?  and is there possibility to make maximum ability of the player?

 

When you lower their age, the player do retain their attributes through natural progression and training.  To make it remain the same even in old age, you will have to freeze the player.

 

You can technically keep players at a certain age forever so you keep them in your team forever such as players having 100-year careers.