I agree 7 weeks you can easily tell on BRs. I can tell pretty easily when they're smaller based on light or dark coloring, but only if I have a batch of brothers and sisters to compare them to. Usually the females are darker and males are lighter. I have two BRs that I was for sure were males, because of the lighter coloring, but since I had no brothers or sisters to compare to I ended up being wrong. Each breeder/hatchery has variations that can make it difficult to tell at young ages. And I believe some are not 100% pure. I have a BR that has darker colored legs and a greenish sheen to her feathers, but other than that looks like a BR and lays BR colored eggs. Also, I have found that with BRs behavior is no indication of male/female, because the females can be just as brave and bossy, and I've had some amazingly sweet roosters. The best indicator is to wait til they're about 7 weeks, and the males will have good sized combs. All my females didn't show bigger combs until they're close to laying. Fred those BRs in the first pic are absolutely beautiful!