I wonder what age Nathan Chen started landing his double axel. He was landing it consistently in novice competition at age 10, and don't intermediate boys usually do them too? So he would have had it before then...
This quote from icenetwork, says he was landing it in intermediate "Nathan Chen, didn't waste any time showing off all he's accomplished since last year, including a very solid double Axel. Clad in a silver metallic shirt and black pants, the petite 9-year-old from Salt Lake City, Utah, won first place in Group B of the intermediate men's qualifying rounds with a 60.25 mark."
So we have a 9-year old landing a double axel...wonder if I can find anything that says he had it as a juvenile. (ETA: Nope, in competiting as a juvenile at nationals -2008- he was doing 1A, of course, that doesn't mean he couldn't do it in practice.)