Most of my cockerels are almost hen sized by about 10 weeks. Silkies are bantam, so are going to be much smaller. They don't have very obvious male specific feathering, just on their shoulders right now. Male saddle feathers don't start to come in until about 10 weeks and can take a few more to be clearly visible.
For example, this is a 10 week old cockerel, male specific feathering just starting to come in. He's a bit smaller than the 3-year old adult hen on the right and is bigger than the 6 month old pullet on the left.
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