I have 10 BO chicks (I think 5 hens / 5 roos) that are 7-8 weeks now. I'm eventually going to be thinning the roos to 1. I'd like to add some straight run black australorps (maybe 3-4). If I buy young chicks and have them in a brooder until they're 5-6 weeks, can I put them in with the older chicks (which would at that point be 13-15 weeks), or is that enough of an age difference that the older would hurt the younger? Thx!!