Look, I absolutely encourage questioning religion and the Bible, but this particular hill is not one I suggest you die on.
Genesis chapter 11 (allegedly) recounts the lineage of Abram. Shem (who was on the ark) lived to be 600. His son Arphaxad lived to be 438. HIS son (Shelah) died at 433. Et cetera. Abram is only eight or nine generations after the Flood, depending on how you count.
To my eye, there's a clear dampening effect on ages after the Flood. Within a dozen or so generations, mostly everybody dies before age 120.
Some of us have actually studied the Bible in depth. It has its contradictions, but IMO this isn't one of them. :)