When we die, we instantly enter another universe in which everything is the same except we're alive. Even to the extent that a line of possible events is avoided to allow a person to live. E.g. A to a person's conscious lying on their death bed, something happens that allows them to get spontaneously better, hence while they die in their current universe, they feel they've never passed and merely got better. Could be the same with old age, maybe eventually the consciousness ends up in a universe where a 'cure' is found for old age etc. I've been almost killed dozens of times and thought about this very question.