To be clear, I’m not advocating that the spurs be used as a definitive answer. It’s just another thing to look at that may or may not help. From what I’ve read, spurs can develop as early as 3 months or as late as 9 months depending on the breed. I haven’t done any research on this breed specifically, though. Of course you have to go based on other signs as well, especially the comb and hackle/saddle feathers, but the only way to be 100% sure is to wait for an egg or a crow, although some people even have hens that crow.