FIZBIT
Songster
I got 3 standard cochins. 1 is very tiny compared to the others and has a different tail and feather growth rate. The one in question is the partridge. Or maybe it's a bantam which would explain the size.
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I just noticed I missed the question in the title, about gender.
None of them look like cockerels to me right now. They might just be too young to be obvious, or they might really be all pullets.
Age? So far they look like pullets, but age will help.
Your Partridge is LF. Look at their legs. LF have legs for days. You can't much see a bantam's legs without digging through the floof.