What does "coon's age" mean?

Also, a dog's age. A very long time, as in I haven't seen Sam in a coon's age, or It's been a dog's age since I went to the ballpark. The first phrase rests on the mistaken idea that raccoons (“coons”) live a long time. The variant may reflect a similar assumption but the true origin is not known. [c. 1835] Also see donkey's years.