In the wild I think mating season is winter to late spring, but unless you have females, and more specifically females in heat then that wouldn't be it. The ages say a lot though, chinchillas go through puberty around 6 months to a year, and can become moody and more dominate. They should level out by a year or two, but for now think of them as a bunch of teenage boys. It's not uncommon though for their personality to be changed from now on (some don't really change but others go from friendly to not wanting to be touched, others go from shy to more outgoing, etc), so don't expect them to go back to being the same chins they were before. The personality change can include no longer wanting a cage mate. If the chins are fighting then you need to separate them, chins can fight to the death. Fur slips, excessive chasing, excessive mounting, pulled fur, or any blood drawn are all red flags for fighting. If no blood is drawn you can try reintroducing them later, once they calm down, but give it time.
