People have said “Why, I haven’t seen you for nigh onto a coon’s age!”, meaning that he hadn’t seen the other for a long time. How long to racoons live? If they don’t have an extraordinary lifespan for a rodent, did people think they did?
Well, for one thing, raccoons aren’t rodents.
From this page/
I’ve thought the same about “donkey’s years”
You know? I know perfectly well what a racoon is. But when I typed the OP I was thinking of a beaver! :smack: I think in medical terms I had what is known as a “brain fart”.
That does seem to be a decent enough life span to account for the phrase.
Thanks.
Ah yes, cerebrus flatululosis. Everyone suffers from that particular ailment every now and again. 
The earlies citation for “coon’s age” in print (so far) is 1843. My reading of that cite and others in the next 10-20 years suggests that it may have been a rather Southern expression.
There is an earlier cite, 1836, for “dog’s years” used in exactly the same way.
If we want to speculate, we could always suspicion that the term “dog year’s” was used by someone who noticed that a “dog year” would be 4-7 years of a human’s life. Thus a “dog year” was a long time. We could then suppose that those colorful, wiley, Southerners morphed it into “a coon’s age” which stuck in the minds of Americans more than “dog’s years.”
Southern expressions just have such a better patter to them than Yankee sayings.