Coon’s age means a very long time. It is an Americanism that has fallen out of favor, and is considered offensive by many people. Coon is slang for raccoon, coined in the mid 1700’s. The term coon’s age was first used in the early 1800’s and in fact, owes its origin to the folk belief that raccoons are long-lived. Raccoons are not truly long-lived, but their fur is quite hardy, which may have given rise to the belief that raccoons live for a long time. Because of the raccoon’s bandit-like appearance with its black mask, striped tail and stealthy nighttime habits, to coon has come to mean to steal or pilfer, though this verb form of the word coon is rarely used. Coon has also been used as a derogatory term for country bumpkins, as well as a racial slur.
The folk belief about racoons’ longevity has been proven incorrect. The origin of the phrase coon’s age is generally unknown to most people. It is usually assumed to be an insult and it is best not to use this term. Examples are difficult to come by, as the term has mostly fallen by the wayside. A coon’s age maybe related to the old English expression, in a crow’s age. Other related phrases are dog’s age and donkey years.
You may meet friends you haven’t seen in a coon’s age. (Lake City News and Post)
To answer your question, I haven’t seen kids playing marbles in a coon’s age. (Houston Chronicle)