That particular usage is hyperbolic, of course.
Age refers to long indefinite period of time, and in particular, it often refers to a lifetime or generation. This can be exemplified by collocations such as Age of Innocence or Quidditch Through the Ages.
In that respect, it is analogous to the Latin saeculum:
A saeculum is a length of time roughly equal to the potential lifetime of a person or the equivalent of the complete renewal of a human population. The term was first used by the Etruscans. Originally it meant the period of time from the moment that something happened (for example the founding of a city) until the point in time that all people who had lived at the first moment had died. At that point a new saeculum would start. According to legend, the gods had allotted a certain number of saecula to every people or civilization; the Etruscans themselves, for example, had been given ten saecula.
Etymonline will tell you that the word had been used in this sense long before it was adopted in English, so I would consider an earliest known use immaterial here (and, it appears to be related to eon).