Counting too high

Yesterday I was driving the kids to school and Will was counting outloud in the backseat. I admit I had kind of tuned him out, but then his voice got very enthusiastic as he came to the climax of his count:

Will [excitedly]: "...ninety-eight, ninety-NINE,... ONE! HUN! DRED!"

Dad: "wow! Will you counted all the way to a hundred?!!"

Will: "yep, I do it all the time" [this is true, I learned this morning, as I told Erin this story]

Dad: "wow, that's really great. you are a very good counter."

Will: "hey, maybe sometime we could count to a hundred together!"

Dad: "yeah, we'll do it. Maybe we could even count to one hundred and one!"

Will: "no, that's too high."