player evolution

[atenista14]

I noticed that every off season some ratings of my best players will decrease. I just would like to ask if the ratings is based on their performance last season or is it with their age?is it because of growing old that makes their ratings lower?

[Spree#8]

Their age and also the hidden attribute in players.dbf file called "Learning". This value controls player's ability to learn and increase his ratings, if it's very low they're probably decreasing.