Going back to one of your other questions, people die early because they waste their energies. In the past, there were people who lived for centuries, since in esoteric science we know that through the conservation of one's forces, one can create the elixir of long life, or the fountain of youth referred to in Yoga and alchemy. On the other hand, those ages in the Bible are also Kabbalistic: they refer to initiatic stages on the path to liberation. 900 is a very elevated number, related with the Ninth Arcanum of the Tarot. Hundreds of years refers to, in this tradition, the initiations of Major Mysteries, which are very serious developments. You can read more about this in the works of Samael Aun Weor.