In general the problem is that when humans enter well into senescence, at some point your body just stops working altogether and it's at that point that basically anything that happens to you next will kill you. Or sometimes it will be nothing at all, and your heart will simply stop in your sleep one night.

This is why when somebody dies 'of old age' it's often not like you can just seem them slowly drifting away day by day. Rather they seem to be in perfectly good health, for their age at least, and then 2 weeks later, they're dead.