[Endoperez]

It would require a new mechanic. It wasn't added during development even though it is a rather generic idea that'd fit many, many races and specific units (EA R'lyeh, void monsters, Atlantis, Agartha, several undead creatures, pretenders such as Ancient Olm, Vampires, Eternal Knights...). I think that means that it was deemed too hard or too complicated to implement, but that's just my educated guess.

Shapechange based on age and reversed stat bonii from old age have both been requested in the mod wish thread, so there's a slight chance of us getting them... However, the mod wishlist thread is huge, and we can't expect to get even half of our ideas implemented.