I agree. Mine started at less than two weeks of age and the girls participated some too... and they're almost 5 weeks now and they still do it some, but it's never serious. Nothing even close to injury. I would say it's very normal behavior. They want to establish a pecking order.
Definately roosters, the hatchery marked the hens for me with red dye on their heads. As the dye wears off I remark with food coloring. I'm going to seperate the hens so I don't lose any. The 30 roosters are just for meat.
They are Silver Laced Wyandottes. Both sexes do a little squabbling, but the roos are definately more aggressive. I expect some pecking order to happen, but to the point of injury surprised me. Hopefully, it was an isolated incident and no more will get wounded.