My ONLY regret with transitioning is that I didn't do this sooner. Childhood transition wouldn't have been an option for me, because of how I was raised. However, I wish more than anything that it was. As for puberty blockers, they were used to help treat gender dysphoria in children, without issue, since 1993. As was stated before, blockers are administered at the onset of puberty (since there is no reason to do so before that) typically around 10-12 years old. Hormone Replacement Therapy (HRT) typically begins at age 16, though sometimes as young as 14, and only with the recommendation of two shrinks AND the permission of said child's parents.