It really depends on how you want to waste your time. If you want to waste your time training his outside skills, he'll never get better but at least he'll still be old. If you want to waste your time training his inside skills, he'll never get better, but at least he'll be old. If you want to waste time with stamina and FT training, he'll perform slightly better but your team as a whole won't progress much.
I'd read through the thread GM-Perpete linked you to. Probably three or four times.