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.
This is exactly what I remember. And as you can see yourself, there is nothing about old age.
For that the most common citation points to the Monstrous Manual (1993) which is for Second Edition and under TSR rather than WotC. It says that Mind Flayers have a lifespan of 125 years.
Also, this^ The game is based on the 5th edition, so I doubt the relevancy of the 2d one, sorry.
Though tbh, I think this is a pretty minor problem for BG3 compared to other plot problems.
Agreed. I also agree to everything else OP stated, so I saw only this one point worth discussing
