How to maintain your players several seasons in your team?

[Grandef]

For example my AML ML I currently have:

390 greens from 47% to 133 % at the age of 19
260 greens from 116% to 163% at the age of 21
230 greens from 113% to 152% at the age of 25

Now he is 26 at 140%, he will play until he is 28 or 29. I replace when a player doesn't have 100% anymore at season start and I don't train players older than 25.

What about the drills you used to train your players? I used the same strategy as yours and at 21 yo, I train grey skills so it took a lot less green to raise %.