I'm no expert...so take it with a grain of salt. I was pretty sure at 3 weeks that I had a roo because his feathering was far behind the others. He had naked shoulders, no tail feathers and tiny little wings whereas the others flight feathers all pretty much reached back to their bums. At 4 weeks I started seeing noticeable difference in his comb and now at 5 weeks it is turning pink. He also has very beefy legs! One of the "girls" may still surprise me tho!