From the White Wolf Wiki, the most complete White Wolf reference

The Ages of Man was first introduced as a concept as the Wheel of Ages in Kindred of the East that described a cyclic view of the history of the World of Darkness. The idea has been loosely adapted by Exalted.

The Ages of Man can be seen as a wheel with twelve segments or a lotus flower with twelve petals, each of which is an era in world history. The First Age of Man was a glorious utopian era, and the Sixth Age of Man will be Hell on Earth. As history progresses, the ages get shorter the closer to the Sixth Age we are, and longer the closer to the First Age. The Ages continue perpetually.

Ages do not change cleanly, although there is usually an event that marks the changing of the ages.

This is one piece among many elements which lead many people to conclude that a connection exists between Exalted and the World of Darkness. If this is indeed the case, it's uncertain if the two settings exist in the same turning of the Wheel or seperate turns. Or, indeed, whether Exalted is the past or the future of the World of Darkness (although most evidence points to Exalted coming first).

[edit] The Ages

• The First Age of Man was an age of glory and wonder.
• The Second Age of Man, also known as the Age of Sorrows (EX: Exalted Rulebook, p XX), was still a fantastic time, but somewhat less Utopian than the First Age. This Age occupies the present of the Exalted setting.
• The Third Age of Man, also known as the Age of Shadows(EX: Exalted: The Autochthonians, p XX).
• The Fourth Age of Man
• The Fifth Age of Man
• The Sixth Age of Man
• The Seventh Age of Man
• The Eighth Age of Man
• The Ninth Age of Man
• The Tenth Age of Man
• The Eleventh Age of Man
• The Twelfth Age of Man is also the First, and here the cycle repeats.