I think it is just really breed dependent. The wyandottes just start early, but in comparison, the males are more prominent earlier on than the females. In the second week, the other chicks were trying to pull the wattles off the wyandottes. My rock pullet had wattle "nubbins" at 3-4 wks, but at 8 weeks really hadn't progressed too much. My RIR roo (avatar) was suspiciously roo in the first week, but by the 3rd week the only thing keeping me from pronouncing him a roo was my denial. Some hens and roos break the "rules" with wattles and combs and this is why pics are so useful, so that we can see the entire bird - comb, wattle, feathers, legs - and decide what sex they are.