Does anyone find it strange that no one in Skyrim walks with a limp? That no one no mater how old or blind uses a cane or walking stick? This is a violent dangerous land yet no one needs crutches or a wheelchair, don't you find that odd? Yes I know there are lots of restoration casters and alchemists, but I dout everyone can afford or has access to them.

Restoration magic. Simple as that.

Also, its easier on development to just make everyone walk the same. Plus, custom animations for a handful of minor NPCs is not high on any developmental priority list.

I actually think this is a pretty good idea for a mod, it's not like Bethesda is going to make it.
Also I'm pretty sure restoration can't heal old age (not sure about the whole wheelchair and crutch thing I'm pretty sure they didnt have those).

Making a mod for this shouldn't be hard, there are already animation mods for just about any action you can think of.