I agree with @OneHappyRooster if they're that age they're pullets. 

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That looks a lot like what happened to Van. The waddles started growing first and then the comb started getting bigger. I still have a brown Legion rooster here he is the same age and is starting to crow. If the Sussex was also a rooster wouldn't they he at each oher trying to determine who is the alfa for the flock? (The leg horn was here first as we got him as a day old and was raised by my araucana)Looking through my bird photos I only have one of a Sussex. She was 13 weeks old.
I'll attach it anyway.
Bear in mind their combs will be changing a LOT during this time. I don't know where the other photos went, but after that age her comb grew very fast.
She is now a broody hen, 4 years old.
Thanks for your reply Marcelle. That's the one I'm suspicious about. I'll check their wings this afternoon when mu husband gets home and look for those longer feathers. I really hope it is a she, as I was told it was a she when I got it but for some reason I've always had my doubts.Hmm....the tail feathers of the lighter coloured one look like a cockerel to me. The cockerels have a wider wing span as well if you can pull their wing span out. They have 2 longer feathers at the end. But one of them does really look like a cockerel...sorry.