Can you solve this Math Puzzle?

A man and his wife are dining at a table in a plush restaurant, and the husband keeps staring at a drunken lady swigging her drink as she sits alone at a nearby table.
The wife asks, "Do you know her?"
"Yes," sighs the husband, "she's my ex-girlfriend. I understand she took to drinking right after we split up seven years ago, and I hear she hasn't been sober since."
"My God!" says the wife. "Who would think a person could go on celebrating that long?"