So you've said he's well balance in other areas - that's your answer right there.

Does he demonstrate concepts -- so does he understand big/little, night/day, boy/girl, that kind of thing? What about colours, shapes.

You really need to consider the big picture and not just one area. So from what you've said about other things, he sounds perfectly normal/fine to me.

What sort of counting activities are you doing with him? I would focus on fun counting rather than sit down rote counting. Like when you are out waking, count the number of dogs you see, mailboxes, that kind of thing.