I have too cockerels that are within 2 weeks of age from each other. One 15 week old RIR, one 13 week old Jersey Giant. The RIR has been EVIL since he was little....the JG was always nice.
The RIR has gotten worse and worse daily, even with me chasing, stomping at him, kicking him, picking him up, etc. Today he "flogged" me when I was leading them back to the garage to get put away. Came right at my ankles as I was about to go down the hill. Once I had him in the garage, he jumped up on a box and then flew at my chest. Crazy frickin rooster. He is leaving in the next day or two to live with a friend who is experienced in aggressive roosters, has no other chickens and will eat him if he can't be retrained. Yum.
My Jersey Giant has always been nice other than a single peck when I made a girl squawk.....it hurt and I instinctively whacked him away and into the coop fence. He learned his lesson and has never pecked me ever ever again. He is a late bloomer and has not even started harassing his girls yet, so he may get cranky as well.