Too old

On Friday, I drove K and D to school. I took D to his classroom, and when he was all settled, I went down the hall to K's room. He had just finished hanging up his backpack and was about to go into his classroom. I said to him, "Your class looks like so much fun--can I come?"
"No, everyone in my class is 4 or 5," he said. "There's no one in my class who's 56!"