Yes, they did live that long. And Santa has a flying sleigh pulled by eight flying reindeer. The Tooth Fairy puts coins under childrens’ pillows. Zeus hurls thunderbolts. The Moon is made of green cheese. There is a pot of gold at the end of the rainbow.
Why would he do that? IIRC, the only distinction Methuselah had was his age. He didn’t do anything spectacular; he was mentioned once in the Bible, because he sired one person in the long line of “begats.”
and,
Why are you using one formula to determine Methuselah’s age and another for Abraham and Sarah?