Getting old

For science (human biology), Mark's reading assignment was called "Getting Old" and was about aging.  I said, "That's appropriate with my 41st birthday approaching."

He didn't respond.

I said, "Mark!  That's when you're supposed to say, 'No, Mom, you're not old.'"

He said, "Well technically, Mom, you are.  Forty is when you officially get old."

I said, "How do you know?  Where did you hear that?"

He said, "A variety of sources."

Guess which one of my children doesn't get any birthday cake?

A variety of sources tells me he doesn't deserve any.