I currently have one 5 year old in my year 1 class who has regularly hit and kicked other children and she is a girl.
It's not a boy thing, it's a development issue.
The child needs to learn empathy. They need to understand that even though it doesn't hurt them it does hurt the other child when they kick, hit, bite, scratch. Until they do, they lash out like preschool children.
By age 5 most, but not all, children have learned that it is wrong, and they are able to control themselves, share and wait their turn. If another child does something to them, rather than retaliate they have learned to tell an adult.
The aggressive behaviour described by the OP is different to 'rough and tumble' play, minor squabbling, snatching toys from each other, etc. Those are all age appropriate issues which children learn to negotiate so that they can play safely together.
I agree with spiderpig that it would be useful to find out the triggers. Are the school recording each incident and what happened just prior to the aggressive behaviour. What other stragies have the school put in place to help him?