Actually, in Elaine's Evermeet book, it seemed more along the lines of "Elven mages tend to get killed by their own spells more often than their enemies do." Read the book again and count the number of times that an elf is killed by one of his own spells. IIRC, it's at least three.
I view it more along the lines of leveling NPCs based on their age category. A starting age npc has one level, a middle age character has 1d6+1 levels (unless they have levels in a PC class, in which it's 3d6+1), and an old age character has 1d6+1d4+1 levels (unless they have levels in a PC class, in which they have 3d6+1d4+1). If they're an arcane casting class and still practice that trade, they'll continue to level, and will have 4d6+1 levels.
A longer-lived race might have +1 levels per age category.
