Welsummer roo's are a different colour to the hens. Some show these colours earlier than others though. Look for black feathers forming on his chest area, and a deep red colour on his back. Also keep an eye out for saddle and hackle feathers. Crowing varies, you can never be sure when they'll start crowing. I've heard of roosters crowing at 8 weeks old, but mine didn't crow until around 3-4 months old.