Dee, the aggressive behaviour and hyperactivity (could it be showing off in front of the other kids?), could possibly be his way of finding his place in the pecking order. Boys tend to "act out" far more than girls, and if they are not finding balance, or order, or if they are unsure or feeling like they don't know where they fit in they tend to use "physical" language more often than not.
My middle child went through a similar thing at one stage - thankfully it didn't last for long. We just went through the "showing off" thing this weekend when his cousin was here (big noting himself, being loud and boistrous, picking on his little brother). He is a very competitive child, and beleive it or not that actually makes it worse, because he feels that he has to be "top dog" in every situation.
Sorry to ramble, but it is such a big subject. Hope that I possibly shed a light somewhere. There were already some great suggestions.
Reach for the moon, at least you'll land among the stars.