I really feel like I was without mental health issues until a suffered trauma that set me on a path of dealing with PTSD, including severe depression and anxiety. These symptoms sort of become a serious issue starting in my 20s, but while I suffered a great deal internally, I was always very high functioning - got my college degree, started my career, long-term marriage, children, etc.
So, I'm one of those, that wouldn't have been recognized at all as having mental health issues by most people watching me function. But internally, I was a mess. I was hospitalized for depression and suicide over a dozen times in my 40s.
But about the time I hit my 50s, I had been through a decade of intensive therapy, responded well, made major changes in my thinking and behaviors, and have not needed therapy or medications now for over 10 years.
Am I cured? Pretty much. I still have to keep an eye on the PTSD. For instance, with the recent death of my husband to Covid, I've had to very deliberately work on some symptoms that cropped up again. I still keep a watch on my depression symptoms, etc. But the difference now is that I am able to see those issues; I know what I need to do to work through them, and I don't find them rising to anywhere near the level they were earlier in my life.
I think there are different types of mental health issues. Some people have lifelong problems that aren't consistently responsive to treatment, or are more long-term disabilities that require a lifetime of focus and treatment. Others have short, very reactive short-term mental health problems that are responsive to brief therapy and sometimes just time. Mine were somewhere in the middle, requiring more than just brief treatment, but responsive to treatment given the right therapist, etc.