I'm going to need to stat up a few elder magi for my saga, but the sourcebooks are drastically short of guidelines for magi of the 100-150 years / archmage level. I'm happy to wave my hands a bit for people outside the covenant, but the senior magi in the covenant need a fair quantity of stats; particularly since they're likely to have written a significant number of the texts in the library!
So, other than doing season-at-a-time (400 seasons!) what can be done?
A good resource for building magi at various power levels is the Magi of Hermes book from Atlas Games.
It presents fifteen Magus characters, with backgrounds and story hooks, but also fully statted at several points in their life: right after their Gauntlet , 15 years later, 30, 60 or 75. It's both a good source of powerful NPCs and a good template for building them.
If you want magi even older than that (75 years active + 15 years of apprenticeship + ~8 years of childhood = ~100 years old), it shouldn't be a problem to check the differences in stats between, say, the +60 years and +75 years versions of the same character to see how much of a bump you should give. Keep in mind, of course, that it gets incredibly hard to raise scores at those ranges, so you should check out the differences between +30 to +45, +45 to +60 and +60 to +75 to see the average rate of slowdown, as well. Or just approximate and give a bump to the stats.
