I agree with Allie Jayne.
In my younger years, I was just too busy. I joined the Army right after my 18th birthday and served almost 15 years. I got married, had kids, got divorced, remarried, and was focused on raising a family. I got injured and went on total disability, my wife got sick and passed away, and I was struggling to make ends meet. I married a third time, started some small businesses for income, and continued to be busy. It wasn't until I divorced wife #3 that I decided to move to South Dakota. I decided that I would no longer have to worry about jobs or family or what anyone else expected of me. I was going to do what I wanted to do.
Since my hectic life had finally calmed down, I was able to focus on taking care of myself. I got into therapy to try to understand why my life followed the path that it did. It was in therapy that I learned that I was transgender. Combining that with other discoveries (I am an asexual introvert) really helped me understand why things happened the way that they did. Being retired gave me the time to invest in examining myself that I never had before.
As we get older, we have more time for reflection and examination, so it makes sense that we would make these discoveries later in life.