Individuals are merely disposable vehicles for the replicating information contained in the genes.
Now, one might argue that the longer the organism lives, the more offspring it can produce, and the more copies of its genes will be made. Hence, the genes of organisms that do not age, and thus live longer, would be naturally selected. Though a gene can make its vehicle or carrier stronger, smarter and more resistent, it can never completely eliminate all possible perturbations causing death. On the other hand, we might imagine genes stopping the process of aging. There are enough examples of self-repair mechanisms in cells and organisms to suggest that this is possible.