They programmed players to have 4 stages:

18,19,20,21: fast training
22,23,24,25: normal training (60% of original)
26,27,28,29: slow training (30% of original)
30,31,32,33,34: slowest training (15% of original)

I had players with 18 years's old who gained over 150% in a game or 250% with man-of-the-match award.