Why would evolution need that? If grandpa is badly adapted, he'll starve/get eaten/etc; no need for a built-in kill switch. In fact, if there were a kill switch getting rid of it would be highly adaptive, if only because you could be around to defend your great-grandchildren.
(Of course, we do die. But the explanation looks more like "growing and reproducing quicker beats longevity" than like "planned obsolescence".)
Grandpa wears out, yet competes for resources. Kill him off, more for the healthy youngsters. Certainly its selective, at the family/community level, choosing to keep more-efficient members.
I also think, making grandparents less mobile means they are around the campfire teaching the youngsters. It makes sense it would be selected for in a race of communicators.
The Darwinist reasoning behind rates of aging goes something like this. A adult mouse has a high chance of being killed in a random year (above 20%) a Parrot has a low chance (below 3%). Maintaining a body into old age has a cost that reduces reproductive capability in a given year and a benefit of increasing the number of years of reproductive capability. There are also minimums of capability in the wild where vision and mobility link to survival rates such that there are thresholds below which rates of survival dramatically decrease.
Thus, the number of healthy years in the wild relates to both the probability of an external death AND internal heath issues. For a mouse this suggests a minimum of internal maintenance for maximum reproduction where a parrot can make significant trade-offs in reproduction in order to live 10x as long and have more long term reproductive chances.
However, that's in the natural setting. A pet (mouse, cat, parrot) can live slightly longer in captivity by surviving pat the point where it can find food for it's self. If you look a human vision decline people are significantly less capable of surviving on their own before they lose reproductive capability. And in that "unnatural" old age it's not uncommon for various species to have increasing reproductive issues.
(Of course, we do die. But the explanation looks more like "growing and reproducing quicker beats longevity" than like "planned obsolescence".)