I started when I was 54, and it took a lot to get myself to the point of 1. understanding I was a trans woman and 2. beginning the transition process.
I came out slowly in stages, starting with my closest friends and then wider and wider circles. I am very lucky to live in the Portland, OR area where acceptance and support is more common than many or most other places in the US, and to work for a company that is welcoming and supportive of trans folks and our healthcare needs.
And yeah, I wish I had started decades ago. But better late than never!