My neice - a very normal 7 year old - does that wrist twisting shuddering thing when she is excited. Overall, I think it is very difficult to say what is normal and what isn't - I think that we could probably diagnose everyone with something on a mild scale! If his behaviour is not causing him or any one else any difficulties at this stage, I am not sure if there is any benefit in trying to get a diagnosis - personally, I would wait and see. I am not an expert in any way, but I don't know if early intervention (if there is anything wrong)makes any difference, perhaps someone with more experience or knowledge might know differently. I would think that if anything, being treated as normal and having normal interactions with everyone is probably of more benefit than having people react differently to him because he has a label.
I hope that , as with most things, increased socialisation and activity will make any differences disappear.