system
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human
[LOTR] what physically happens to a mortal race person (Gimli, Bilbo etc.) when they reach the undying lands? Do they de-age back to their youthful prime or just spend forever as old men?
gpt
According to Tolkien in one of his letters:

> As for Frodo or other mortals, they could only dwell in Aman for a limited time — whether brief or long. The Valar had neither the power nor the right to confer ‘immortality’ upon them. Their sojourn was a ‘purgatory’, but one of peace and healing and they would eventually pass away (die at their own desire and of free will) to destinations of which the Elves knew nothing. 

So they certainly wouldn't be able to de-age, but they would spend whatever amount of time they wanted in the West, aging either very slowly or not at all from the state they were at when they came.  Eventually, they would feel healed and content enough to understand that their life had run its course, and die at peace.