What breed is this chicken? Brown Leghorn?

[PajamaGardener]

We got a batch of chicks from tractor supply on Sept 10th. We got 6 - 3 Easter Eggers, 2 Barred Rock, and 1 that was supposed to be an ISA Brown. The single chick was bigger than the others and had some feathers when we got them, so I think it was about a week older than the others. As it has grown, I don’t think it is an ISA Brown. Right now I’m guessing it’s between 5-6 weeks. It is very skittish compared to the others. I’m just at a loss as to what it is. Please take a look at the pictures and see what you think. It’s also looking more like a rooster to me, but time will tell.

He looks very similar to my barnevelder. Maybe an olive egger?