"It was after the great flood that we had the Caine and Abel incident."
Uh no it wasn't. Cain and Able were the first 2 sons ever, and they did not go on the ark.
Anyway, when God placed te curse on all of creation he withdrew some of his sustaining power. Up until that point God was the source and giver of eternal life. Just as I believe he would have prevented Adam falling and breaking a bone or similar.
Since some of the sustaining power is removed things now circle in decay and in time fall apart.
From a genetic point of view, age is dictated by the genes and specifically how many times a cell is allowed to replicate before it stops and dies. When Noah got on the ark and the world was flooded a huge amount of the human race's genetic code also drowned. I believe Noah was unable to pass on the genetic code he had that allowed him to live to an old age, because of degenerate mutations. Adam and Eve's body's were perfect, but every generation since then has more and more decay and mutations mixed in with it. We don't evolve, we actually devolve.
Can God allow a man to live to an old age of 900 now? Certainly he can. Will he? I doubt it highly.
No amount of naming it and claiming it will achieve what God does not see fit to do.