We are a commune of inquiring, skeptical, politically centrist, capitalist, anglophile, traditionalist New England Yankee humans, humanoids, and animals with many interests beyond and above politics. Each of us has had a high-school education (or GED), but all had ADD so didn't pay attention very well, especially the dogs. Each one of us does "try my best to be just like I am," and none of us enjoys working for others, including for Maggie, from whom we receive neither a nickel nor a dime. Freedom from nags, cranks, government, do-gooders, control-freaks and idiots is all that we ask for.
Sometimes you end up wondering who is more crazy - the MSM, or the lunatics. Or the politicians.
Almost everybody had a friend or an acquaintance who unraveled and became psychotic during late adolescence. I had a friend who did, first year of college. Still my friend, but he is a shell of a person. Too sad for words, and an eternal heartache for his parents. He was a star athlete and a math wiz, and now he can hardly feed himself or dress properly, and studies asteroids hitting the earth shut up in his room except when old friends take him out for lunch.
Of course, those asteroids might hit - but who cares? Who has time to worry about that? It's like worrying about Global Warming. Daily life beckons. Don't worry, be happy.
Only one personal experience in support of your proposition that going over the edge in the late teens or early 20's is common. I saw it while in the service. It was sad and to be there when it happened was nothing less than scary. He survived from what I know and my last communication was that he was pursuing a meaningful life.
My bet is you are really right about the frequency of this and no census or mental health survey is ever going to catch how often it does happen.
Sometimes life is just damn sad and we have to deal with it as best as we can.
I don't know about teen/young-adult psychosis, or whether or not it's common ...
... but the attitude that this particular "psychotic" should be 'handed over to the shrinks' bothers me. A lot. Here's why: Usually when I hear about a 'psychotic with a gun' case, the psycho fires off a lot of rounds almost at random, and gets relatively few hits. One in five, one in ten, something like that. This worm was carrying a 9mm with a high-capacity magazine, and he killed six and wounded thirteen without reloading. Nineteen hits out of thirty (or fewer) rounds says to me that he wasn't firing at random. He was picking his targets and taking time to aim. That makes it deliberate, intentional, with malice aforethought. A better example of someone who deserves the death penalty would be hard to find.