My chicks are about the same age. I do not see them pecking each other, but they do like to jump at each other...like their cock fighting each other. It could be a period of molting. I don't know if you can mites on chickens like I can with my bees.
My young chickens are losing their feathers, mainly near their wings and along their sternum -abdominal region. I'm new with keeping chickens, but it might be mites. I looked, but did not see any. Maybe mites are too small to see with the naked eye. These chicks are 4-6 weeks old, maybe older...