How Young We Are

Ethan wrote these numbers.
He said, "4 is Ethan, 55 ('five five') is Daddy and Mummy and 1 is Jethro."
I had a strong suspicion what he meant, but I still wanted to make sure. So I asked him, "What does 5 mean?" He gave some random answer.
So I tried again,"Why am I 5?"
This time he said it: "Because you are 5."
"5 years old?" I grinned. He nodded.
"Is 5 bigger than 4?"
"Yeah," was the immediate reply.