I have had multiple players < 25y/o have a downward pop (outside of stamina). Driving (21y/o 5 to 4), handling (23 y/o 6 to 5) and rebounding (24 y/o 7 to 6). The next time I trained them, they popped back up, so there is a minimal decrease potential every week. There were no injuries or over playing in these situations that I remember.