It shoudn't be so difficult, in order to not penalize managers that want's to train, they can link perfomance to the ages of the players. Till 27 yo no penalty, from 28 yo a penalty increasing with the age of the players till a maximum penalty around 32 yo (just for example of course, put your figures)
1990-2022 Stalinorgel - https://www.youtube.com/watch?v=pV-Xppl6h8Et