Ok so technicaly not a teen

[ACMDowding]

but I keep getting told that "there's a teenage section".

I am having the usual problems with DS1(stroppiness, answering back etc). Yesterday though he hit a mindee, not hard, but he hit him.
Of course he has been punished and made to apologise to mindee and mindees parents.
However, it was sinply because he got annoyed, the child is 3. DS1 isn't, and I feel that he should be better able to deal with an (extremely) annoying 3 year old without resorting to violence. He has a tendency to fly off the handle though over what are (in our opinion) silly wee things. is this normal and can I please have some advice on how to deal with it