How much space do they have? Do they have plenty of roosts? Sometimes overcrowding can lead to fighting at a young age. If there is blood loss/visible wounds then you should keep an eye on the wounds, the others may start cannibalizing them. Hard habit to break once they start doing it. The bully and the injured bird may need to be separated and isolated for a while. Blu-kote works great to hide blood and wounds. Neosporin (plain, no pain relief) works great to help heal up injuries too.
I don't free range my keets until they are 12 weeks (personal preference, due to their hawk and ground predator vulnerability prior to that age). Some start a lot sooner tho. If you can sit with them and keep an eye on them, and successfully herd them back in to the coop when it's time to go in... then you can start whenever you feel they are ready to free range. Successfully herding them back in each evening and making it a normal routine is crucial tho if you plan on locking them up each night for safety (highly recommended). I would not just turn them loose at any age, you may never see them again.