I made a flippant comment about "my first 39th birthday." Little Boo scoffed and replied, "You can only have one 39th birthday, Mommy. Then it's 40th."
I explained that big grown-up mommies often have lots of 39th birthdays because they don't want to get any older.
"But they still get older, Mommy! You can't stop that. Silly mommies."
He just doesn't get it, does he?