First of all I want to point out that from the viewpoint of evolution (self perpetuation and genetic adaptation, survival of the fittest etc.) there is no need for an organism to live past reproduction other than to help raise the newborns. Therefore there is a genetic predisposition for death by old age. In other words, we are genetically programmed to die after a certain amount of time.
Take for example the octopus. After they grow to adulthood and reproduce, both the male and female die after about a month (senescence). The female will lay her eggs and then tend to them, keeping them oxygenated and protected. During this time she eats nothing and has been known to eat one of her legs for sustenance. Once the eggs hatch she slowly becomes dumb and dies.
The cause was found out to be a genetically programmed excretion of a substance from the optic gland which is adjacent to the optic lobes which controls sexual maturity and aging (among other things). If this gland is removed after reproduction the octopus resumes feeding and survives far longer than usual.
I think its pretty safe to say that most if not all organisms have a genetically programmed senescence state which when triggered causes the body to gradually die (senility?). The above article explains a link between DNA methylation and the senescence of cells. It makes sense but what does that mean for us? Will we be able to alter the methylation of certain genes in the future? and how?