Being 140 years old is a pretty defining character trait. Should definitely be an Aspect referencing that. How does he feel about new technology, new philosophies, new takes on old religions...? Does he have random old-fashioned skills?
You'll also want an Aspect referencing the cult specifically, so the GM has something to Compel when they want to draw you into a fight with them.
Something referencing a long history and a lot of regrets might be good too. If you've been a lot of places, done a lot of things, and made a lot of mistakes, it opens up a lot of space for Invokes and Compels. Might overlap too much with I'VE SEEN WORSE THAN THAT, though.
If you want phrasings, I suggest LIVING FOSSIL, VENGEANCE FOR <son's name>, and A CENTURY OF REGRETS.