[(E)]

I've played with the Ageing based idea before, good for big magic. It worked best in a solo game where the pace of the game wasn't held up by the characters down time. I had a custom advantage "age backwards while asleep" with a couple of add ons like works better at ley lines and crystal sleep chambers. Note beware dark and evil sorcerers with acne whose voices are breaking.

Another one I have played with but not implimented is a centralized power source for all the (official) mages in an empire. Both these ideas are written up as threads here somewhere.