I think I have a Roo. Help!

[Cindy in PA]

I would say pullet. I think most of my single combed breeds had much more comb going on further back on their heads & I could tell for sure by 3-4 weeks. Just a guess though. If it sprouts a lot more in a few days, you will know.

 

[debid]

The size of the comb looks well within the range of normal and there's no color to it yet. It also has only a single copy of the barring gene as evidenced by its coloring. Either this is a pullet or it isn't actually a barred Rock.

 

[Eryniel]

I found this thread to be helpful.
https://www.backyardchickens.com/threads/sight-sexing-barred-plymouth-rock-chicks-at-hatch.798635/