I have been searching the web for similar advice. My daughter just turned 6, and has been doing the hand flapping, or "flapping her wings" as we call it, since she was 2 months old! She does it when she is happy or excited. Sometimes she will lay down and flap her hands and her feet. Sometimes she makes a blowing noise with her mouth when she does it, too. I have always known it is a sign of Autism, but she is definitely not Autistic. However....she has been showing me more and more signs of probably a problem dealing with emotions. I have been searching the web for advice on this- hoping to find something about how to teach your kids coping mechanisms. I deal with what are probably similar stimulation/sensory/emotion problems. I use a lot of breathing techniques and take time to find a quite spot when I feel over stimulated. I watch her start getting irritable and over stimulated just like I do, but I am not sure if deep breathing will help a 6 yr old?
Anyway, Im not sure what else you see in your little one, but in my endeavors to find answers to my questions, I have found LOTS of info on hand flapping- and I find that the general consensus is too let him do it, don't take it away from him or make him feel like you dont accept it because it is a sensation that makes them feel good. Some articles have been addressing what to do if they are being teased at school about doing it, and they still have said to let him keep doing it and dont discourage it, but rather help your child come up with a response to the teasing.
This website helped me a lot- mostly the comments at the bottom. There are several comments posted at the bottom from hand flappers themselves, which helped me to have some insight on why she actually does it in the first place.
As a former parent of a child with autism (my late son was high-functioning) I would like to reiterate that autism is NOT always obvious. You have probably seen children with ASDs and not known; stuff is not always going to jump out at you. You're also used to your son's particular traits and behavior so even if he's displaying other signs, you may not notice them. My son was highly verbal, had an extremely high IQ and made good eye contact. He could also carry on a conversation and play with other children. I would have him evaluated; get a referral for someone who specializes in children with ASDs. Being easily distracted can be an indicator, but honestly there's no "one" cue. It's more a whole-behavior picture and pattern of behavior. The fact that you call him sensitive is also resonating with me.
Sarah-Wife to Kelly, mostly organic crafty SAHMama to my angel, Canaan (11/01/07-03/15/2013) and Ezra (05-12-09).