Yup, I'm with aapomp on this one. I normally tell people to wait until the chick in question crows, or lays an egg. But I have some Barred Plymouth Rocks again this year, and coincidentally, they all just turned 8 weeks. Here is a photo of one of them. Very confidant he is a Roo, for the same reasons:
View attachment 2751867
As aapomp said, he is larger, much lighter, and developed his comb long before the others did, and it's much larger than his sister's. He also is showing consistant specific behavior I would expect from a Roo - first out in the morning, last in at night, sits on a perch and watches over the others while they eat, does "tidbitting", gave a warning when my wife showed up on the golf cart, and is constantly swallowing things he should not. I had to pull a long piece of weatherstripping out of his throat two weeks ago, and he has been attacking the silicon installation on the Juvenile coop and swallowing it. Tough little guy, for sure.
I'm thrilled, as I am currently in between roosters, and so far, he seems like he is going to be a good one.
Other things - does yours have larger thicker legs compared to the others, and a comb larger and redder, that developed before the others developed theirs? Saddle and sickle feathers will typically start to develop in another month or so.
They make nice looking birds - here is a mature Barred Rock Rooster:
View attachment 2751877
If you cannot keep one legally, then by all means find him a good home. But if not, consider keeping him. They are typically good Roos, and not knuckleheads as other breeds can be.