Wing (feather) sexing is only possible if you breed for it. You have to breed fast feathering to slow feathering, which will produce the fast or slow feathering offspring on the opposite sex. For example, if you breed a fast feathering roo to slow feathering hens, the female chicks would be fast feathering and the males would be slow feathering. I did not select for this in developing our lavender Orpington, so it is unlikely this would be very a effective way to sex them unless the person you got them from selected their breeders in order to match them up this way. Typically you can tell your cockerels from pullets pretty well by 6-8 weeks old.