Life (aging) is a direct cause of cancer. And we can't change that unless we have some sort of nanobots constantly repairing DNA damage in every single cell of our body.
We both expose ourselves to too Many toxins, eat too often, and don't get the right balance of nutrients over the long term.
If you can positively impact these things, then you can lengthen health span and lifespan.
Life (aging) is a direct cause of death. And we can’t change that. Might as well die.
But if people didn't age, then there would still be a base rate of mortality from illness and accidents, and so for any arbitrary probability (99.9%, etc) there would be a maximum age that one could reasonably expect to live to.
For instance, if the only thing people ever died of was car accidents, at a rate of 20 per 100,000 people per year, then it would still be very unlikely for anyone to live more than 20,000 years. That's a long time, but it's not millions or billions of years, much less eternity.
Furthermore, if nothing but accidents killed people we might become extremely conservative and do practically nothing for thousands of years. Do I want to use the stairs and risk 99% of my potential lifespan?
So maybe one could say that biology and even physics don't ensure death, probability does.