From a different perspective....
I adopt chickens (both genders). They all come with their own stories. I have several rooster flocks.
The cockerels start coming into their hormones around 4 months old. Some later. Very seldom earlier.
Some boys handle puberty very well and others are PMS'ing 24/7.
When it comes to mating, almost all start off rough. I teach them to be gentle. I sometimes supervise. (And no, boys don't like to be watched or talked to while they are mating. But I don't want them tearing up my girls, so I will intervene if they are too violent.)
Younger boys with older girls is fine. Most of the times, the girls will put the young man in his place.
I'd be concerned about the young man mating with the 5 month old girls. Depending on the breed and their maturity, they may not be ready for mating yet.
Puberty (and all the behaviors that go with it) will continue until he is about a year old. Some settle down sooner and others continue the hormonal roller coaster a bit longer.
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When I felt things were getting out of hand (boy too rough on girl), I removed the boy.
Some of my guys the rooster flocks will violent jump a girl who wanders into their turf. They can't seem to help themselves cuz they are so horny.
I have two young men (haven't reached the 1 year mark yet) that were just too big and too violent with the ladies, so they didn't get a flock. They go after the ducks now. The girl ducks are a bit submissive if they are caught. The boy ducks are like, "QUACK, oh quack quack NO!" and will BOTH chase after the horny chicken. Normally, I don't allow a gang up, but in this case, I don't stop it. The young men need to learn that it's not ok. I also put the young men in time out. That seems to have helped some. (They stopped going after the girls and started going after the boys. The chickens tend to avoid me now, so catching them for time out is a bit harder.)
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Based on experiences, I wouldn't cull the young man yet. You will be going through the same type of experience when the younger guys come into hormones.
Could you separate out the young man? Keep it so he can see the girls, eat through the fence with the girls, but not mate with the girls? Separate sleeping quarters? He will mellow out with time.