Sounds fairly normal at 4 months. The more dominant often suppresses the behaviors of the younger boys. Some may not even enter puberty by then. Each chicken is different. If they free range and have a lot of room it is possible they may always get along and not cause any problems with your girls. Or when the hormones hit both, they may seriously fight. Sometimes those can be fights to the death (usually not with lots of room), sometimes they reach an accommodation. It's possible they can each claim a territory away from each other and attract whatever females they can. There are all kinds of possibilities of what might happen. Since they are in a run now, the bigger your run is the more likely a good outcome.
That's what is supposed to happen, if there is conflict he runs away and stays away. That is where room is important. He has to have enough room to get away and enough room to avoid the others. How big is that run? I don't mean these square feet numbers you often read about on here, does he have enough room to run away and stay away? Clutter (things to block line of sight and give him something to hide under, behind, or over) can improve the quality of the room you have.
I agree with the others, you should have a plan where you can isolate him on a moment's notice if it gets bad. Some skirmishing isn't too bad but if you see any injury or blood I'd separate him. But make your decisions based on what you see, not what might possibly happen. If you see him squatting down and one of the others standing over him and pecking at his head intervene immediately. That can be fatal.
They can be bullies, whether the same age or older. That's how they set up the pecking order. The dominant cockerel or rooster are usually at the top of the pecking order but not always. Some pullets hens can really be strong willed. The less dominant cockerels or roosters can sometimes be outranked by the hens. Each chicken is an individual with its own personality and will fit in the pecking order where they fit in.
I guess my point is that those dynamics could easily change, especially while they’re so young. But I also think you just have to learn as you go a little because all flocks and chickens are different. Good luck!
