in Genesis (6,3)
God decides just b4 the flood henceforth to limit Man's Lifespan to 120 years..
((...his days shall be a hundred and twenty years))

Further on However, i Note in GEneSis (11,10-32)
That The Ten Descendants of NOAH had lifespans that range 4m 148 to 600Years

The 1st passage Genesis (6,3) is a Yahvist text, Probably datin as i have already seen 4m the tenth Century B.C

The 2nd passage in Genesis (11,10-32) is Much More recent Text (sixth century B.C )
From the sacerdotal version.

This Version is at the Origin of These Genealogies which are precise in Their InformatioN on Lifespans as they are taken improbable when Taken EN MASSE