Hard choice. I if I had transitioned much earlier in my life, say around 11 when I was first... outed, I suppose is the right term, then my life would have gone down a drastically different course. But, I was embarrassed and humiliated, so instead of grasping what was offered to me in those few brief minutes, I pushed away the hand that was reaching out to me. That may have been a mistake at the time, and it changed the course of my life immensely. But those years, with the good and the bad (a lot more bad than good for sure) shaped me into the woman I am today.
I did find some happiness in those years. I learned to about my passion, the piano, and picked up a few extra instruments on the side. And all of those experiences, the anger, the frustration, the disappointments; all helped me come closer to my family than I probably would have ever been in any other circumstance. My family is very dear to me, and I would not want to live in world where I am any less close to them than I am today.
No, I would not choose to transition that much earlier. Perhaps 18-19 would have been perfect, but now I am 25, so I'm not all that late. But ages 10-17'ish were VERY important years of my life.