I've not begun HRT, had any surgeries, nor have I had any legal changes. But clothing, binding/packing, hair, and introducing myself by my real (male) name started halfway through 8th grade when I was 14.
I just realized I've only been fulltime for a year now (feels like longer, damn you time XD), since I went into 9th grade "dressed the part" and am going into 10th now. (I plan on asking the teachers to call me Christopher. I didn't get the balls to ask for "Chris" until 2nd semester of 9th.)