Mind flayers live up to about 125-135 years.
Where does this come from? Mind Flayers usually don't die of old age, I doubt they age at all. Mind Flyer can evolve further to become a part of the Elder Brain - the base part or some additional alongside others.
This is all from the BG3 lore, I don't know if some common DnD lore contradicts this.
It's common DnD lore. In DnD, becoming part of the elder brain is actually a Mind Flayer's 'death ritual', and the Elder brains actually hide the nature of what happens. It's sold to Mind Flayers as a sort of 'afterlife' where they become one with the elder brain, when in reality it's much more like the mind flayer's personality is discarded and destroyed and their thoughts and memories are consumed.
At least - this is what I remember from the last time I checked on the lore. Things might have been changed or retconned since then. Another issue going by the lore, if I remember right, is that gnomes are actually immune to ceremorphosis. Well, not immune, but it just kills the gnome rather than making a mind flayer. I forget the exact reasoning for this. (Maybe gnomes are just so small that people kept asking "But where does all the extra body mass come from when they transform?!" But then there should be the same issue with halflings.)
Though tbh, I think this is a pretty minor problem for BG3 compared to other plot problems. I am willing to acccept the official lore being fudged a bit.
