The roosters tend to get thicker legs quickly, their combs/wattles grow out faster, and they have an upright posture compared to the pullets. I'm 99% sure that you have a little girl there.
okay, here's a pic of mine. I think she's a he, he's different than the others. From the very beginning it stands up straight and has a bigger comb than the others and has the tail thing going on.
I think you might have a rooster the pic of him at 4 weeks his legs are a lot bigger than the other one in the pic and the comb looks a lot like one of my roos at that age. His are just now turning red and he is 12 weeks, he was a late bloomer
Here are some LB photos. These are at about 5 weeks. She is 20 weeks now and laying eggs. I have more pictures further along if you want them. Yours looks like a pullet to me.