Ahhhh testosterone. Tis a beautiful thing. NOT. It can turn a gentle, beautiful rooster into a fire breathing claw bearing demon during spring mating season, especially when it is their first season as top cock in the flock. I truly doubt if his change of behavior has anything to do with the younger cockerels. My roosters are very good with the young juvenile males. It's once that rotten testosterone kicks in that things get interesting. I would expect him to be more aggressive towards the new competition then than with you.
Sounds like he needs some attitude adjustment. It isn't easy. I have a LOT of roosters and I don't take any nonsense from any of them...something like 20 of the little heathens.
My first advice is to never go into the coop or run without a big long stick and don't let him get close to you. If he does, push him away with the stick. Always walk purposefully towards him like you own him, the hens, the whole darned coop, which you do. Don't show fear and don't be afraid to protect yourself...remember, you have the stick.
What I do with my boys is if they show any attitude towards me, I pin them down and I grab them by the feet so I can dangle them up side down until they relax. When they do relax, I swing them up and carry them under my arm like a football, being careful to keep hold of his feet with that hand. After carrying them for 15 minutes, I place them on the ground and push them down until their chests meet the dirt. That is the submissive pose for a rooster. If he fights, repeat everything until he relaxes and allows you to be dominate to him.
I've never had this method fail for me and it was one that I found on BYC.
I make it a point to keep that long stick nearby and when I finally let the rooster up, a whack on his bottom sends him on his way and reminds him to stay out of my reach.
It will take a while to get the message across to him but hopefully he will learn to stay out of your way. I have 15 bantam roosters right now. 10 adults and 5 juveniles. All OEGB. All known to be little demons and they are with one another. But with me they are perfect angels. I also have 6 standard sized rooster....oops, that's 21, lol. The standards know to get out of my way when I enter the coop or run.
No reason to put up with attitude from an aggressive rooster. If he doesn't settle down with his aggression, you have young boys in the wings and once they mature you can choose the best for your girls, and for you!
Good luck! Let us know how it goes.