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Having a relationship with an elderly person. Dating outside of an age group.
Charlie: "I don't see Elroy around much these days."

Filbert: "Oh, no. He's off downtown with a group of geezers. He's into carbon dating now."
Charlie: "I just saw Elroy with this ancient looking bird. I think his new game is carbon dating."
by El Bicho April 10, 2010
Dating between two people of dissimilar ages, generally an older man and a younger woman.
Did you see that old guy on her arm? I know she's desperate but I didn't think she'd sink to carbon dating.
by Sterling T December 26, 2006
When a really old man dates a really young woman.
Hugh Hefner's new girlfriend is 25--looks like they're carbon dating.
by ll00l0l January 19, 2011