The Bible clearly teaches that people in the Preflood World lived over 900 years. Josephus, in The Antiquities of the Jews, explains how it was possible to live that long at that time:
Now when Noah had lived three hundred and fifty years after the Flood, and that all that time happily, he died, having lived the number of nine hundred and fifty years: but let no one, upon comparing the lives of the ancients with our lives, and with the few years which we now live, think that what we have said of them is false; or make the shortness of our lives at present an argument that neither did they attain to so long a duration of life; for those ancients were beloved of God and [lately] made by God himself; and because their food was then fitter for the prolongation of life, might well live so great a number of years; and besides, God, afforded them a longer time of life on account of their virtue and the good use they made of it in astronomical and geometrical discoveries, which would not have afforded the time of foretelling [the periods of the stars] unless they had lived six hundred years; for the Great Year is completed in that interval. (Source: Josephus. The Complete Works. Translated by William Whiston. pp. 39-40)
It appears that in the Preflood World there must have existed far more nutritious food which provided men with a greater number of vitamins making all those who ate it extremely healthy. We often wonder how it was possible for the ancient civilizations to build such awesome structures like the Pyramids. If we assume that the ancients lived over 900 years and the knowledge about the movements of the celestial objects was passed by them to the future generations, we can easily come up with an answer to such questions. Of course, throughout history there were always certain groups of people, who decided to keep this knowledge as a secret and used it against their subjects in order to keep them in constant fear and darkness just like Pharaohs did.
Josephus states that some ancients historians also confirm that the people before the Worldwide Flood used to live over 900 years:
Now I have for witnesses to what I have said, all those that have written Antiquities, both among the Greeks and barbarians; for even Manetho, who wrote the Egyptian History, and Berosus, who collected the Chaldean Monuments, and Mochus and Hestiaeus, and besides these, Hieronymus the Egyptian, and those who composed the Phoenician History, agree to what I here say: Hesiod also, and Hecataeus, Hellanicus, and Acusilaus; and besides these, Ephorus and Nicolaus relate that the ancients lived a thousand years; but as to these matters let everyone look upon them as he thinks fit. (Source: Josephus. The Complete Works. Translated by William Whiston. pp. 39-40)
Why would ancient historians write that the people before the Worldwide Flood used to live over 900 years? Maybe because the people before the Worldwide Flood really used to live over 900 years. Josephus’s statement serves as a powerful support for every Bible believing Christian because it proves the Book of Genesis is historically correct.