The Waste is an unspecific amount of generations old, however Nirnasha mentions millenniums have passed since it's creation meaning it is at least two thousand years old. Tšatši created it using the SunFyre, which created the vast desert the Waste is currently. All who were captured within it died but still lived as reanimated corpses. Nirnasha explains this is the case because the magic was based off of the Sun, which can both give life and kill.
The Waste is a desert, with it's sky grayed out so much that the sun is nothing but a pale disc in the sky. The sand, however, is still a normal gold. It is littered with bones and mounds, under which the Guardians are buried. The edges of the Waste are bordered by the raging Tempest. There are fewer Guardians near the Tempest, and more at the center of the Waste.