I'm not a TS, so that title doesn't apply.
But for first TG? Well, that sort of depends on threshold.
Probably around the age of 7 or so-ish, I remember my mom going on how long and strong my nails were. I just couldn't be bothered to cut them all the time. I didn't really care about any gender overtones.
Also around that age, my sister and I borrowed my mom's house shoes. They were soft, so they were fun to wear. I didn't really care what they looked liked so much, or that they had any gender attached. My mom wanted us to stop, though. XD
Around 10-11, I remember being really drawn to a shiny poodle skirt my mom made for my sister. One time I was alone in the house, I decided to wear it. I wasn't really sure what to do from there, but I did some spins and other movement. It felt great. I was very conscious of the gender associations, but I don't think I ever felt like it was making me a girl or anything, just that it was forbidden.