My would do that when he was very excited until he was about 7 or 8. He told us he did it when he felt he had excess energy that he had to get rid of and he got excited about so many things then--books, games, playing video games with friends, playing with friends in his musical theater class. I remember being a little embarrassed once when he did this in front of someone and they said something about it. It seems that a lot of people automatically think little kid using adult vocabulary plus reading at 2 plus flapping when excited equals Aspergers. It didn't matter that a developmental pediatrician and neuropsychologist said he did not have it. He does have some sensory processing issues that I thought were just overexcitabilities and motor dyspraxia.
He paid more attention to his appearance and changed the flapping to a more socially acceptable and less obvious rubbing his hands together at age nine.
At 11, he is much more reserved and conscious of his front stage/back stage appearance. He liked reading about sociology a few years ago and when he read about dramaturgy it really clicked for him that he needed to play a normal person in real life and save being himself for back stage. Back stage is much more fun or it used to be until other things in his life took away some of his ability to have fun.
