Unfortunately, for people who are predisposed, going away to college or falling in love can also trigger a psychotic break. I don't think we would tell people not to do those things though.
I would bet that people who are predisposed to e.g. schizophrenia are, for the most part, going to experience some insult that makes it come on at some point before 30 years old. It's just a question of when, where, what, but it'll happen.
I bet the group of people who could develop schizophrenia were they to experience the right insult, but don't, is very small.