I had no idea I was autistic. I was sent to psycologists when I was in my early 20s because I was a mess. They wondered if I was developing schizophrenia. Or bipolar disorder. Or a personality disorder. I had OCD and seemed to have PTSD. They were puzzled because I was clearly ill but didn't fit any catagory. Many members of my family were similarly afflicted so it was put down to bring "highly strung" and one more in a family of eccentric artists. I was given SSRIs and beta blockers and left to my own devices. When my sister had a son he was obviously similar but being the first boy in two generations his symptoms were different (and in some ways more overt). By the time he was 9 or 10 he was having real problems. My sister pushed for getting him help (when I was a child my parents, both on the spectrum, were less than useless and the school were clueless, autism barely being recognised even in professional circles at the time) and he was diagnosed and statemented. As the family became clued up on Asperger's it became glaringly obvious I had it. (As did my father, mother, maternal grandmother, paternal great uncle, a cousin, my maternal aunt, and two second cousins.)
I wasn't diagnosed as a child because it wasn't a "thing". I was just a peculiar child, eccentric, obsessive, desperately anxious, highly intelligent, socially awkward, unhappy and desperately trying to fit in, always walking to the beat of my own drum. Years later the same teachers who taught me taught my nephew (it was a small island community with a small school) and they told my sister that now they understood the condition better it was obvious what had been "wrong" with me. One of then was quite distressed looking back on how I had been treated, saying " we just didn't know".
I've not gone looking for a formal diagnosis. If I was working in the mainstream I probably would as I found working in the mainstream so difficult. I have instead become self employed, allowing me to construct a working pattern and environment that I can mostly cope with. When I had mainstream jobs I lurched from burnout to burnout and was constantly ill with anxiety. Nowadays people see me as a slightly odd but successful artist and tattoo studio owner. I do mask but allow enough of my real self out to stop myself being overstressed. People just put it down to being an eccentric artist and don't seem to mind. I cope pretty well as long as I keep within my own parameters and am allowed to use my coping methods. As I've got older I've become much less self conscious and more insistent about addressing my needs. If I ever ended up in a situation where I had to go back into mainstream employment I would seek a formal diagnosis in order to take advantage of any and all help I was entitled to.