The Six Ages of the World (Sex aetates mundi; also Seven Ages of the World, Septem aetates mundi), was a Christian historical periodization scheme first written about by Saint Augustine circa 400 CE in De catechizandis rudibus (On the catechizing of the uninstructed), Chapter 22.
"was based upon Christian religious events, from the creation of Adam to the events of Revelation. The six ages of history, with each age (Latin: aetas) lasting approximately 1,000 years, were widely believed and in use throughout the Middle Ages, and until the Enlightenment, the writing of history was mostly the filling out of all or some part of this outline.
"The outline accounts for Seven Ages, just as there are seven days of the week, with the Seventh Age being eternal rest after the Final Judgement and End Times, just as the seventh day of the week is reserved for rest. It was normally called the Six Ages of the World because in Augustine's schema they were the ages of the world, of history, while the Seventh Age was not of this world but, as Bede later elaborated, ran parallel to the six ages of the world. Augustine's presentation deliberately counters chiliastic and millennial ideas that the Seventh Age, World to Come, would come after the sixth. . . .
"Augustine was not the first to conceive of the Six Ages, which had its roots in the Jewish tradition, but he was the first Christian to write about it, and as his ideas became central to the church so did his authority.
The theory originated from a passage in II Peter:
"Medieval Christian scholars believed it was possible to determine the overall time of human history, starting with Adam, by counting forward how long each generation had lived up to the time of Jesus, based on the ages recorded in the Bible. While the exact age of the earth was a matter of biblical interpretive debate, it was generally agreed man was somewhere in the last and final thousand years, the Sixth Age, and the final Seventh Age could happen at any time. The world was seen as an old place, the future would be much shorter than the past, a common image was of the world growing old.
"While Augustine was the first to write of the Six Ages, early Christians prior to Augustine found no end of evidence in the Jewish traditions of the Old Testament, and initially set the date for the End of the World at the year 500. Hippolytus said that the measurements of the Ark of the Covenant added up to five and one-half cubits, meaning five and a half thousand years. Since Jesus had been born in the "sixth hour", or halfway through a day (or, five hundred years into an Age), and since five kingdoms (five thousand years) had already fallen according to Revelation, plus the half day of Jesus (the body of Jesus replacing the Ark of the Jews), it meant that five-thousand five-hundred years had already passed when Jesus was born and another 500 years would mark the end of the world. An alternative scheme had set the date to the year 202, but when this date passed without event, people expected the end in the year 500.
"By the 3rd century, Christians no longer believed the "End of the Ages" would occur in their lifetime, as was common among the earliest Christians" (Wikipedia article on Six Ages of the World, accessed 10-26-2014).