One theory of aging in Bleach

Because this has been bouncing around my head for a while, gaining bits, and it's about time to write it down.

I'm not entirely sure that character age is one of the things KT thought all the way out, but I think he had at least a basic idea of how this was supposed to work; what little info we have on aging in Soul Society does suggest a certain shape of rationale, and he's consistent about it.

( Spoilers, obviously )

So there's my theory, based on what we've seen so far. Of course, this suggests that Ichigo's appearance in spiritual form may settle at late teens or early twenties while his material body keeps aging, which could be fodder for all kinds of interesting future-fic.