That's what I originally thought because of his eye color, however there is no concave on his shell and the anus is placed closer to the shell instead of further like it would be on a male
I would have said female because the cloaca is close to the body. And you can usually see a little thumb-sized indentation in the middle of the plastron on a male.
Completely flat plastron... No doubting that. I am glad to see I wasn't the only one having issues. I've read that there have been males without the indentation but I've read that females can have red eyes! Although hers are more of a brown then red.
Yes. If your outside habitat is fairly large, box turtles get along ok with others of their species. But if you crowd them into a smallish habitat, Territory fighting will occur no matter what sex they are.