I think that is generally true, but with some lines apparently it can be the opposite. My australorps didn't feather out that fast, and still had pretty tiny tail feathers, but I'm pretty sure they're both hens. I also have a white wyandotte who was about 2-3 weeks behind on the feathering and who I was positive was a roo up until about 8 weeks old when she started feathering out and I put her photos up here and I had 9/9 people tell me she is in fact a hen! So I wouldnt make a decision just yet, wait a couple of weeks and see how he/she looks then!