I was 27 when I started telling people (soberly) how I felt, and that was also the year I saw my GP about it and started hormones.
I had always felt it inside though and up until the point I allowed myself to accept it I had been desperately unhappy and lost.
It is NEVER too late to realise and do the things you need to do though. I know a guy who only told people and started doing something about it when he was 54 and now he's the happiest 56 year old I know