I've heard people (mostly children) calling dibs on things since I was a little girl back in the early 1950s.

I just asked a group of 8-year-olds, "What does it mean when you Call dibs on something?"

One child answered, "It means you get to have it because you called dibs before anybody else."

Funny. I need to ask the kids in my next class--after such an answer--"Well, what exactly do you think 'dibs' means?"