When I was officially diagnosed, I was about 24 years old.
I need to qualify this statement. Back in those days, they didn't call it PTSD. It was called something like "hysterical something or other." They only called it PTSD within these past 20 years or so.
I have been seeing mental health professionals since I was about 6-7 years old. But I didn't really learn a lot, because I had no way to talk to them, and most of what they said to me made no sense. I didn't speak until I had been in the hospital about 6 months. They had to reset bones, and get me healthy enough to survive, as well as teach me basics on how behave like a human.
When I was 24 years old is when my children were kidnapped, and afterwards I lost all will to live. So, they placed me in the state mental hospital for the insane. I was there for a couple of years. Once they wiped my memory, I became another person whom they created and then I was able to go back out into the world again.
Unfortunately, over the years, bits and pieces of my memory came back. usually at the wrong times and places. My PTSD Cup was full and overflowing most of the time, and I had no clue why.
Due to repeated trauma and lots of bad incidents in life, it was difficult to get on an even keel in life. Plus, when you add multiplicity into the mix. . . well, lets just say life sucked big time.
I think I was in my late 40s before I finally figured out how to find peace. Not that I didn't try, because I tried every thing I could think of to have peace in my life.