You know by D&D rules its perfectly plausible to have a young adult reach epic status, where they can potentially challenge established epic NPCs like, say, Manshoon.
They probably didnt want to give many options for extended life in order to be "realistic". I mean we already have so many heroes, kings, VIPs, dying in novels and such, and its like "HELLO 5k gp nets you a raise dead spell! You are the goddamn king of corymr or something!".
They probably didnt want people doing the same thing about VIPs not drinking the potion/casting that spell/whatever.
Ioulaem's longeveity's radius is about the size of a city i believe. For some reason Ioulaem decided to transfer his soul into a illithid elder brain, and thats his current form for like a few hundred/thousand years? Oh while doing so he faked his death so his lover would get pissed and retaliate at the mind flayers by casting Ioulaem's longevity in their city, wiping it out, and destroying all copies of the spell(except the one ioulaem has, and the one she has i believe).
There has to be a seriously good novel behind this story. I hope there is.