Just remember, once you’re over the hill you begin to pick up speed. – Charles Schulz
I’m not sure what it is about getting older that really is disturbing. Other than getting closer to death, in estimated years. No one really knows how much time they have. In that way the years themselves should not matter. I think it would be far too creepy to know when or how you are to die. It could change your whole life and then change even that too.
Write about a character who was told their time and method of death and how all that changes when they are in an accident and realize it was all wrong. What regrets might they have about their life and all the time and plans they made expecting they knew how to avoid death or how much time they had before death was an issue for them.