I don't know about mental illness necessarily starting during early adulthoood or late teen years...I thought that was specifically schizophrenia(though apparently in rare cases it can start sooner). I don't think in my case I will regain a healthy mental state considering I didn't exactly ever have one.

So the way I see it is I just want to manage my crap, not sure why it's incurable...though some argue their mental illness is not incurable so maybe it depends on the person, what they have and other factors.