When cockerels reach the age where they're getting ready to assume roosterly type duties, they can get an overload of hormones. By this time, you should be pretty well set in which ones you're going to keep, and which pullets/hens you're going to pair them with. You may already have each of them established in with their respective flock. This would be the time you change a bit of your habits in the coop situation. Always walk straight up to the cockerel/rooster, and get him moving out of your way. Don't chase him, just walk, and get him moving away from you. Then continue with coop chores.
At some point, one of the cockerels may challenge you. NO, it does not necessarily mean it's going to be human aggressive. It means it's overloaded with hormones, instead of good sense. The very first time this happens, get a "rooster stick". It can be a broom handle, a long piece of 1 x 3, a sturdy stick. The rooster stick is not to hurt him with, but to increase your reach. Your arms are only so long. Immediately, go straight up to him, and tap him, not too hard, on the butt. You are training, not trying to hurt him. As he moves out of your way, keep the pressure on. Continue following him. If he slows down, tap his butt again. Don't worry about the pullet/hen commotion. Keep him moving out of your way, for a few minutes. Don't overtire him. Now, let him come to a stop. Is he giving you stink eye? Is he putting more weight on one foot? If so, get him moving again for a few minutes. Now, go into the coop area, like you're going to do chores. Walk around a little more, then leave the coop/run, making sure he does NOT try to sneak up behind you. Repeat this for about a week. Now, you should be able to go into the coop/run, walk over to him, and he'll move out of your way, then you can do normal coop activities. He should resume doing chicken things, like scratching the ground, calling his hens, etc. You should be able to walk quickly behind him, and catch him, at least once a week, then set him down, and he goes off, to resume his normal activities.
Once you've done this, at this age, things usually go fine, and you can safely do coop chores without concern. There should be no more aggression with one exception. I would NOT grab any of the hens, to check them over, without him being penned. I check mine over routinely. I dust them if needed, worm as needed, etc. There is always going to be that one hen, that sounds like she's about to be tortured, or killed when you first pick her up. Even if she settles down, the squawks can, and will trigger a cockerel/rooster. It's their JOB to protect their ladies. I always start with the cockerel/rooster. Once, I'm finished with him, I pen him up, so he can't get to me. I have a door between my coop, and run. It's easy to finish with him, then put him in the coop, shut the door, and continue with the females in the run. A dog crate works well for this too. Normally, because he's experienced it first, even when the hens initially fuss, and he's in "protect" mode, he will quickly settle down when the hen does, and he sees you're doing the same thing to them that you did to him. Once you are done, checking them over, worming, dusting, etc. and you are finished with the last pullet/hen, he can come back out. He won't hold a grudge.