Welcome to BYC!
 I'm glad you joined us.
 
You're correct, Golden Laced Wyandottes (and all varieties of Wyandottes in general) should have rose combs. Occasionally, hatchery-quality birds pop up with single combs, but that isn't all that common.
 
Male Wyandottes will develop combs faster than the pullets will. By the time they are 6 weeks old or so (and I sometimes notice it beginning at 4 weeks), the cockerels will usually have obviously redder, larger combs than the pullets. However, Wyandotte combs will not get as large as those of single combed breeds. Width of comb is another good indicator of whether a bird is a cockerel. Wider combs almost always belong to cockerels.
 
Because I've raised Wyandottes for a couple of years, I can usually tell cockerels from pullets at 6 weeks old or sooner, based on comb size, width, and reddness. The males often also have thicker legs, a taller stance, and broader heads. By the time they are about 4 months old, cockerels will have developed saddle feathers and pointy hackle feathers (pullets never get saddle feathers and have blunt neck feathers).
 
With that said, Wyandottes can be tricky to sex some of the time. Last year, I had a Wyandotte that at 4 weeks old, already had a large, red, wide comb. I thought for sure that I had a cockerel and was thinking of selling it, because I didn't need another male. But when the time came to sell it, I realized that I actually had a pullet! The comb didn't get any redder or larger from 4 weeks to 8 weeks. Since then, I'm always a little more doubtful on whether I have a cockerel or a pullet Wyandotte.