No mortal knows how long this Age lasted, nor do they know for certain how it came to an end, and in general most surviving references that date from the Age or shortly thereafter are dubious. The only thing most historians of the Third Age of Stability will accept about this time period is that it existed and the world was a much different place. With that in mind, it is best to take a look at what this Age is accepted to be.
The Age of God Wars was a period, a minimum of two millennia long, during which the gods of many different Pantheons walked the Sister Continents in physical form, demanding worship from the varied peoples of the world. The gods did not (for the most part) live upon the Sister Continents, but rather traveled back and forth from their home planes of existence. The gods of the more powerful Pantheons could do this more or less at will (still requiring effort) while lesser Pantheons required prayer from their followers, which could range from a handful to thousands, in order to reach the Sister Continents.
During this time there was always conflict between the Pantheons, but as the gods became more adept at traveiing to the Sister Continents, and they became more powerful and more curious, a monumental shift occurred which resulted in open and constant warfare between the major Pantheons, with the lesser Pantheons caught between. The cause of this escalation is of considerable debate with two preeminent points of view. Many point to a text known as the Ôxêum Codex, which dates from the Age, that sites an incident where the King-Priest of Ȥmokon was murdered by a god at the behest of Ûxu-Kîm priests while the two nations were allied. According to the Codex, this murder begins a long chain of events that pits all the major Pantheons against one another in a war for domination of the Sister Continents. The Tomes of the Touched on the other hand seem to suggest that this murder was a small event centuries distant from the catalyst moment. The Tomes are a difficult to translate and more difficult to understand compilation of ramblings by a man many believe to have been insane, but they claim that the War began as the most powerful Pantheons searched for a mysterious object.
Whether you prescribe to either of these or to one of a hundred other theories, what is known for fact is that the Age came to an abrupt and violent end that in one manner or another barred the gods from taking physical form on the Sister Continents. In this instant in time, seismic events shifted the lands of the Sister Continents, entire populations disappeared, and vast quantities of knowledge were lost during the First Forgetting (aka The Great Banishing), presumed to be very similar to the Forgetting spoken of at the beginning of the Age of Stability.
Those who survived this rending of the Sister Continents entered what is now known as the Age of Warlords.