It all adds up

My wife was having a conversation with The FMO (age four-and-a-half) the other day:

FMO: "Mommy, is one hundred and three the biggest number?"

Wife: "No, honey. You can add one to one hundred and three and get one hundred and four. Infinity is the biggest number."

*pause*

FMO (with furrowed brow): "*How* old is Daddy?"