At 7 months old he was still a cockerel, not a rooster. At that stage they're often basically idiot teenagers whose hormones do most of their thinking for them.
If you do want a rooster in your flock - and some folks will disagree but personally I think there are far more, and better, reasons to have one than "only" if you want to hatch chicks - then there's a couple of options I'd suggest.
One: get an older (18-24 months +) rooster from someone you trust to tell the truth about his previous behaviour and why they're rehoming him. Here, I'd look for either someone with an established multi-generation flock who was looking to have a few less boys around the place, or a breeder looking to retire an older cock in order to bring in new blood. The best options available where you are might be different.
Two: buy some hatching eggs or chicks from someone who breeds for temperament as well as other traits. Ideally have a broody raise them, or at least try to have them in with your older birds as soon as possible. The older girls *should* clobber some sense into them once they hit the terrible teens but if not, you could always separate them into a bachelor group for a couple of months if you end up with more than one boy. See who's the nicest - and who your hens like best - when they've grown up and calmed down a bit and you reintroduce them to the main flock, and cull the others unless you end up with a pair that are both really nice and seem to get on fine together.
