I am pretty sure that is not cheating , this is the game engine behavior with new training method... my example, I bought an 18 years old player and played and trained him constantly and individually using greens(only specific training), and after almost 3 seasons looks like below,
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So... on non key attributes there was a slightly increase, but the key attributes increased dramatically.
As a conclusion, after 6 more seasons the non key values will remain the same and will be reported as 1%... , as someone said maybe is better to keep players and not sell them on age 22. .