the player's trainability decreases as their skill (quality) increases - yes
trainability decreases with age -yes

But in special cases where a manager invests all SP into roles and QA, the trainability will still decrease with age even though the Q is not increasing. Correct?
- yes, but remember that a player 18-21 y.o. has about the same gaining.
So, if you invest in a 5* player in sa & extra position, you level up and this player become a 4* player, his gaining will increase.
This is because q in training counts by the stars !
Read this post #185
http://forum.topeleven.com/tutorials...-chris-19.html