A country term referring to a period of time roughly equal to 10-15 years, but really just means a long time. Similar to coon's age.
(From "The Waterboy")
Mama: "Why you home so early, my precious angel?"
Bobby Boucher: "Mama, somethin' bad
Mama: "Somebody hurt you, my boy? Who hurt
you? You tell Mama who hurt you."
Bobby Boucher: "Nobody, Mama. It's just that...I lost my position as the team's
water distribution engineer."
Mama: "Why, that's the best news I've heard in a dog's age. Now you be able to spend your days at home where you belong."