It's not a gender thing. All real silkies are supposed to have those big walnut combs but a few of mine have single combs and pea combs. That just means they aren't pure silkie. You can't really tell when they are little (I think). I can't, maybe a chicken expert can?
I have pictures of when my silkies were about 5 weeks old and I can tell you what their combs looked like.
When they are a little bigger you can tell what ones will have walnut combs. They will have like an imprint on their forehead.
This little guy grew up to have a walnut comb. It looks kinda like a thumbprint.
This is him before I gave him away at 16 weeks
This silkie grew up to be a pullet with a walnut comb.
Silkies that will get single combs will look like this
Then this is what a silkie with a pea comb will look like.
The one on the right has the pea comb.
Phew, I'm sorry for the quality on some of the pictures but they were all I could find. I hope I helped.