About Gods of Destruction and lifespans

[nineko]

There's something that doesn't sound right to me.

We know that Beerus has been alive for millions of years, and yet, Whis is looking for potential replacements for him, so much that he asked both Goku and Vegeta if they were interested. The problem is that they can't live much longer than a century or so (as said in another topic the other day, a few centuries at most).

Does the lifespan of a mortal get bumped up when said mortal is officially promoted to a divine role?

If so, why do Gods of Destruction need replacements at all? If their lifespans get extended (either by their Angels or by, why not, using the Dragon Balls), what prevents them from repeating this process forever?

That is, unless they retire voluntarily because they're bored of the job, otherwise I see no reason for e.g. Belmod to wish to be a few million years younger instead of training Toppo to replace him.

[WittyUsername]

The way deities work in the Dragon Ball universe has never been well defined. Most of the gods are apparently capable of getting old and dying, but they have such ridiculously long lifespans that they might as well be immortal.

[Yuji]

Belmod's only been a God of Destruction for a couple of thousand years compared to Beerus' millions. The lore is vague enough but it seems GoDs are just previous mortals who take up the job and are then imbued with a divine lifespan. I'm sure the lifespan isn't infinite but it's probably so large retirement is optional.