Half-Elven Lifespan

[Bearcat]

I'd say that Cerilian halfelves would typically live for the same amount of
time as a standard AD&D elf.

[Craig Greeson]

Greetings,
One of the players in my campaign wants to create a 1/2 elf regent of
Dhoesone. As we were discussing this character, a question came up about the
expected lifespan of a 1/2 elf on Cerilia. The standard AD&D 1/2 elf (IIRC)
typically lives less than 50% as long as their elven parent would expect to.
However, even if a Cerilian 1/2 elf has only 10% of the infinite life span of
a full-blooded elf, I believe that would still technically be infinite. Is there
an official rule for this somewhere that I'm missing?
If there's not any official info. on this subject, I'm leaning toward
giving my 1/2 elves a "choice" similar to the one given in Tolkien's Middle Earth.
At some point when they are relatively young, the children of a joint human/elven
marriage (or "liaison", for that matter) must decide whether they want to be mortal
or immortal. Those that choose mortality would have a significantly longer life
span than a standard human (maybe 300-400 yrs.), but they would age and eventually
pass from the mortal world. 1/2 elves that chose immortality would be more readily
accepted by the Sidhelien, while those who chose to be mortal would tend to live
with humans. Only mortal 1/2 elves would be able to be priests, reflecting the fact
they had accepted the human way of life.
Any rule clarifications or comments would be welcomed.

Thanks for your help
Craig Greeson