You can find Seth's explanation, for example in the session #902, from "Dreams, “Evolution,” and Value Fulfillment, Volume One: A Seth Book"
https://books.google.com/books?id=P4g...
"... Chapter 5 of Genesis to learn what great ages are given to Adam and nine of his descendants up to Noah, or the time of the Flood. Did Adam really live for 930 years, or Seth, the third son of Adam and Eve, for 912? (Why isn’t Eve’s age given in the Bible?) Enoch, the fifth elder listed after Seth, lived for a mere 365 years, but sired Methuselah, who at 969 years is the oldest individual recorded in the Bible. Methuselah was the father of Lamech (777 years), who was the father of Noah (950 years).
In Genesis 11, the listing of Abraham’s ancestors begins after the Flood with the oldest son of Noah, Shem, living some 600 years. Generally, Abraham’s forebears didn’t live as long as Adam’s descendants had, although after Shem their ages still ranged from 148 years to 460. Abraham himself was “only” 175 years old at his death"
In those early days men and women did live to ages that would amaze today—many living to be several hundred years old. This was due to the fact that their knowledge was desperately needed, and their experience. They were held in veneration, and they cast their knowledge into songs and stories that were memorized throughout the years. Beside this, however, their energy was utilized in a different fashion than is today: They alternated between the waking and dream states, and while asleep they did not age as quickly. Their bodily processes slowed. Although this was true, their dreaming mental processes did not slow down. There was a much greater communication in the dream state, so that some lessons were taught during dreams, while others were taught in the waking condition. There was a greater and greater body of knowledge to be transmitted as physical existence continued, for they did not transmit private knowledge only, but the entire body of knowledge that belonged to the group as a whole.