OLD AND CRAZY --BUT AT LEAST YOU'LL HAVE YOUR HEALTH: Derek Lowe has been doing some reading --and some more reading-- and he has the depressing theorizing on the ossification of our personalities, though it doesn't have to happen like that, he points out. He also has good stuff on mental illness:

There are only a set number of ways in which humans go insane. Think of any given case of dementia, and you can come up with plenty of similar ones: you have paranoids convinced that their thoughts are being read - by their TV, by aliens, by invisible beams - or that the people they see on the street are all agents. There are the people who let piles of paper and garbage crowd them out of their houses. And the obsessives convinced that they are good friends with, are going to marry, are already married to some celebrity. You'll certainly find differences among these and among the many other types. But they're variations on the same master templates, differences of degree rather than kind.

Those templates sound like archetypes. Maybe.