It is a cockerel! I checked for spurs this morning, and it has small ones growing in. And I don't know if all you guys notice a difference in the way your pullets and cockerels sound (like when they cluck), but this one sounded like a cockerel to me.
This is probably silly to ask with a 4.5 month old Silkie, I used to think it was a cockerel but now I'm thinking pullet? Silkies really confuse me! But (s)he's definitely not as roo-ish as some other ones that I know are cockerels. @MysteryChicken