People exist who are try to deny the fact that our first fathers (Adam, Seth, etc.) used to live for centuries.  They allege that the years mentioned in those chapters are really "months" or "moons". The only base for their absurd hypothesis is that if the number of years mentioned in the Bible for the antediluvian patriarchs ages is divided by 12, the result is a number of years "more acceptable" to them.
    As an example they show that if  930 years, the biblical age of Adam, is divided by 12 the quotient is 77 years.  If Methuselah's age ( 969 ) is divided by 12 months the quotient is almost 81 years, and so on.
    When human beings want to deny God, or the authority of the Bible, they appeal to any nonsense, without using discernment, logic or scientific methods. Mankind made up this hypothesis and clothed it with the cloak of science.
    These "enlightened ones" who thought they found the "explanation" of the longevity of the patriarchs, didn't make any effort in reasoning even superficially the issue. That's why they charged against this passage wantonly and irresponsibly, thinking joyfully, that they have "discovered" a flaw in the Scriptures or in its interpretations.  That is why they solemnly declare that in this passage the "so called" years, were just "moons" or "months". They declare all this without noticing that before their own eyes is the denial of their foolish hypothesis. Let us read Gen 5: 3-17.

                 "3 And Adam lived an hundred and thirty years, and begat a son in his
        own likeness, after his image, and called his name Seth. 4 And the days of
        Adam after he had begotten Seth were eight hundred years; and he begat
        sons and daughters. 5 And all the days that Adam lived were nine hundred
        and thirty years; and  he died.
               6 And Seth lived an hundred and five years, and begat Enos. 7 And Seth
        lived after he begat Enos eight hundred and seven years, and begat sons and
        daughters. 8 And all the days of Seth were nine hundred and twelve years;
        and he died.
              9 And Enos lived ninety years, and begat Cainan. 10 And Enos lived after he
        begat Cainan eight hundred and fifteen years, and begat sons and daughters.
        11 And all the days of Enos were nine hundred and five years.  And he died.
              12 And Cainan lived seventy years, and begat Mahalaleel. 13 And Cainan
        lived after he begat Mahalaleel eight hundred and forty years, and begat sons
        and daughters. 14 And all the days of Cainan were nine hundred and ten
        years; and he died.
             15 And Mahalaleel lived sixty and five years, and begat Jared. 16 And
        Mahalaleel lived after he begat Jared eight hundred and thirty years, and
        begat sons and daughters.  17 And all the days of Mahalaleel were eight
        hundred ninety and five years; and he died."

    Let's use a little math:  130 moons divided by 12 = 10.8 years;  105 moons divided by 12 = 8.75 years;  90 moons divided by 12= 7.5 years;  70 moons divided by 12 = 5.8 years; and 65 moons divided by 12= 5.41 years.
    If what these "enlightened ones" say is true, then Adam, according to verse 3, had a son when he was almost eleven years old; Seth had his first born when he was less than nine (verse 6);  Enos when he was less than eight (verse 9); Cainan when he was almost six years old, (verse 12); and Mahaleel had a son when he was just five and a half years old, according to verse 15. As we can see their hypothesis is absolutely illogical, and not scientific.
    It is evident that not everyone who claims to be a scientist or to use scientific methods, is saying the truth.  True science and true religion have to coincide, because true science can only discover what God has created, and true religion  can say only what God said.  What some people forget is that when our first fathers were 500 years old, they were as strong as an actual 35 or 40 years old man.
    The saddest thing of all this is that  "Christian leaders" exist who believe these nonsensical hypothesis.  Sure enough, many years ago I was taken by surprise when my Sunday School teacher, who was a medical doctor said: "With the knowledge I have of the human body I can assure you that nobody can live that long".  Immediately he went to the blackboard and started to divide the total age of each patriarch by twelve, to "demonstrate" that the "so called" years were really "months" or "moons".
    When I went to the blackboard and divided by twelve the age at which those patriarchs had their first son, the only argument that came to his mind was to say: "Well, in different eras they counted time in different ways". Then I replied: "We are talking about the same passage, the same verse, and even the same man, not of different eras".
    It is very common that the hypertrophic ego of many brothers preclude them from rectifying in private, much less in public.  This man was a  Christian, he was not trying to harm the faith. His problem was that he had stuffed his mind with lots of pseudo scientific hypothesis.  Sadly with the authority he had by virtue of being a  medical doctor and a Sunday School teacher, he was unwillingly harming the faith of his brethren, who knew he was a scientist and an honest man.  Sure enough, he was honest, but was honestly wrong, and the teachings of those brothers who are honestly wrong, are the worst of all.