Aging

My sister in law turns 50 today. (Happy Birthday Cathy!) Kori and I were talking about her upcoming birthday on Saturday. Here was our conversation:

Kori: How old is Aunt Cathy going to be?
Me: 50.

Kori: Wow! That's pretty old.
Me: I guess so.

Kori: Whoa, she's going to be a grandma soon huh?
Me: Oh man, I hope not.

I relayed this story to Cathy, she didn't find as much humor in it as I did. Wonder why????