What is the scientific meaning of "Natural death" or "death due to old age"?

Answer 1

That means your body just stops working. There is no trauma involved, not even the ones like heart attack or stroke that people associate with old age, and you don't have to be senile . . . you're alive one moment, and then you're not,

Answer 2

To scientifically explain death due to old age ,a new theory of evolution is required.That would be a theory of inverse evolution.
There is a degradation in humans cells and genetics.This type of degradation is very involved and requires a science dedicated to that study.
Man in the way he is structured should not degrade an then die.
There is something wrong in that type of evolution. The question is what is it.

Neverthe less humans die after a certain amount of time . In Biblical pre Noah days they lived a very long time compared to to day.No Scientific answer were given to explain it.

One scientific explanation I can give is that we all die the same way. It is blood that sustains the life that exists in the brain.
If the pump that get the blood circulating fails that the brain can no longer sustain biological life.

So death occurs when the heart(the pump inherent to all humans) stops.