An interesting thought experiment sent to me an email:
Could the great ages of Adam, Methusela and Noah be real if they were due to being more closely related to Adam and later when Adam’s offspring intermarried with the existing population the mix of genes or loss of Adam and Eves genes led to shorter lives?
This requires some suspension of disbelief. But what if Adam and Eve did have better genetics than us, that allowed them to age more slowly. Could this scenario be worked out so that the longevity of individuals of their lineage would steadily decrease as they interbred with others?