Another interesting philosophical question from the Stephaniec factory.
I thought about this for quite a while because of course I made such a strong declaration of this fact back when I was 4 or 5 that my parents took the (in the 1960's) almost unheard of step of allowing me to grow up expressing my female identity.
As I have often explained I hit an unexpected bump in the road in 1976 when the UK doctors refused me treatment until I was 21. However that brief sojourn as outwardly male if anything only reinforced the certainty that whatever else I was I wasn't male.
So in one sense I would say all of my life. However if I am honest my gender identity only really mattered to me when my body didn't match my expectations. While I had male dangly bits I was always trying to project my female identity. As soon as my lower half had been rearranged that almost seemed to cease to matter. That might sound odd so let me try to explain.
I reached a point in my own head where there was no conflict between what I was physically and mentally, and at that point I was at perfect peace with myself so that everyone else's perceptions and opinions of me became instantly completely irrelevant and powerless to touch that.
30+ years on I can honestly say I really could not care less what I am. I'm just me, and I like being me. I'm comfortable being me, I can't imagine being anything else, so in a strange way I almost struggle now to understand what its like to have that need to be seen in a particular way. It just never occurs to me that I could ever be any different, and in some ways I wonder if this is in fact fairly close to a cis mentality. That's why in my head, at least, I now think of myself as having a trans history and a pseudo-cis present.
Maybe this is what happens when you become ultra longterm post everything. If so I wish you all the chance to experience it because it feels great.