It's normal for a pullet to start getting a red comb at 4 months old. However, the bird in question does not appear to have a single comb. We need a much better picture to make this determination.
I'm not an expert and I don't claim to know it all but there is a difference between the two birds. The first picture was when he was 3 months. I hope this helps.
I am confident it is a cockerel because hens only start to develop large combs when they are extremely close to laying eggs and since your bird is 3-4 months old it won't be laying eggs anytime soon. Also the bird in question has light barring which is a characteristic of Barred Rock cockerels.
I think it might be a hen. The pictures of a different barred rock showed how large its comb all ready was when yours was about the same age as it. I don't see much of a rooster tail on it either. Hope this helps!
well does that explains why my hens are being so mean to it?? i had to save the poor thing and take it out of the coop because they where being so mean and running it in to the fences and pecking it like crazy