There is no theological basis for the concept of earth ages, but those who believe in them agree that the first earth age occurred sometime between Creation and the expulsion of Lucifer from heaven. The first earth age is one of three phases in God's plan.
During the first earth age, man lived in spirit only; there was no physical body other than the soul in which man existed. Spirit bodies enshrined souls. After Lucifer’s expulsion, God destroyed the Earth. The soul bodies, left unharmed, remained for use in the second earth age, which started with the creation of Adam and continues to this day. It is the age of the physical body. The third and final earth phase commences when God establishes the Kingdom of Heaven on Earth, and it lasts for eternity.