A whole chain of things need to happen for you to die, but they typically culminate in starving the brain of nutrients or oxygen. That usually happens due to or

A whole chain of things need to happen for you to die, but they typically culminate in starving the brain of nutrients or oxygen. That usually happens due to organ failure, and that can certainly be the eventual consequence of old age. So tying 'cause of death' to a single factor is almost always a gross oversimplification. There are many causes for every death, and it's only important to look at specific ones should you care to prevent them or assign blame for them.