They get to their max potential too early and they then ''overload'' and the CA starts going down but it takes time....Once I made a player with the editor I gave him 200 CA and 200 PA and 10 seasons passed and his CA only dropped by 1.
Try not to overload your young players. At least untill they are 19 or 20. Give them time to peak. I had problem with one youngster named Garcia. Had 188PA and 110CA in the beginning, and after 3 seasons, his CA increased by 20 oO) ( he was 15 when I bought him). He played almost every game. Then I started to give him a rest, loan him a little and next thing you know, he is world class winger
That's good then, I was worried he might not reach his full potential. But he scores like 2 a game and wins me alot so I need him. But then again, I don't want to rest him because he might lose that consistency that he's showing. :S