[Archonsod]

Never had an age problem with Abyssia. Death or Growth scales both help (so far I've only ever seen disease kill an oldster, so unless your unlucky enough to get feebleminded it's not a problem under either scale).
Another option is to get into the Death path and simply undead your mages, through whichever spell is most convenient. Nature can also be a viable counter if you find yourself with plenty of nature gems (a single pick in nature is usually enough to knock the mage below old age level).