Personally I didn't have a moment when I decided I wanted to be female, all my life I've taken it as read that I'm female, there was never any doubt about that.
However at age 22 I found the courage to face up to the world and start taking hormones.
Afterwards, it wasn't really me who decided the rest, but people around me. Once I started getting quizzical looks and lots of 'Miss'es I just realised I had stepped over the line and my body image had become female.
A good example, was when I was still living as a male, was washing my hands in the public loos and a man who walked in had total shock on his face, apologised and ran out again. When I walked out a few minutes later he was stood in front of the Gents and Ladies looking very confused...
With HRT and facial hair removal (if necessary) things just evolved naturally; I went from boyish male, to fairly androgynous, to tomboyish female, to female... There was no real day in particular when I went from boy to girl, though once I'd stepped over to the female side I changed my name officially and told my boss to stop using my old name...
MVER XXX