By the age we currently stop being 'useful' as members of clan human, i.e. retirement, our forefathers in an evolutionary sense could already have been (great) great grandfathers. Our life as a pensionado or geriatric patient is already a form of life extension, an extra age compared to the stages we used to go through.
Evolution doesn't mean only what is useful stays, it is only when selected for under evolutionary pressure that things are forced to go a certain way, and only after many generations.
The uselessness of old age will only affect evolution if A) there will be a society that is mad enough to really 'do something about it' and B) such a society will eventually outcompete other ways of life and its values start to dominate.
I can imagine a politics where money spend on welfare and healthcare for elderly is minimized to such an extent that life expectancy starts dropping significantly. In a way, the US has something like such a 'make money or die' politics and indeed, life expectancy there is quite a bit lower than would you would expect from such as prosperous nation. Can be economically effective. But it competes which economies where people are productive at an older age, being more focused on staying healthy and significantly less stressed.
Evolution doesn't mean only what is useful stays, it is only when selected for under evolutionary pressure that things are forced to go a certain way, and only after many generations.
The uselessness of old age will only affect evolution if A) there will be a society that is mad enough to really 'do something about it' and B) such a society will eventually outcompete other ways of life and its values start to dominate.
I can imagine a politics where money spend on welfare and healthcare for elderly is minimized to such an extent that life expectancy starts dropping significantly. In a way, the US has something like such a 'make money or die' politics and indeed, life expectancy there is quite a bit lower than would you would expect from such as prosperous nation. Can be economically effective. But it competes which economies where people are productive at an older age, being more focused on staying healthy and significantly less stressed.