But people never select for "good" elderly so to speak.
Neither do most primates or lions. The elders just happen to be there. So we can't really even say if it's just more elders in the animal kingdom making themselves useful. Which, again, is happening after reproduction typically.
For something to have an effect on reproduction, I would think it would need to be part of the decision beforehand.
These sorts of selections are likely to happen on a group level to the best of my knowledge, and you can easily imagine how selection for good elderly could work if you imagine children's life expectancy being dependent on their parents and grandparents. If (hyper simplified) a mutation that allows people to maintain eyesight for an extra 10 years helps them be extra spotters for the family on the hunt, and in a food scare environment, making one kill is life or death for the children's ability to eat, then that lineage with better eyesight could be selected for
Direct fitness is not the only way natural selection favours individuals. Genes that make individuals past their reproductive age turn into good caretakers (including genes that improve their health) are more likely to increase their frequency in subsequent generations (through the descendants they care for). This is called kin selection.
Kin selection. The elderly can help their grandchildren survive, so genetic predispositions towards living longer and helping your grandchildren can propagate depending on the cost-benefit of that strategy.
Likely a very new concept on an evolutionary timescale, and competing against the survival chance cost of more mouths to feed during an acute resource shortage.
It seems absolutely not a coincidence that the much faster, by orders of magnitude, process of human history got set in motion at a time when grandpatenting, as an evolutionary concept, wasn't quite finished yet.
Neither do most primates or lions. The elders just happen to be there. So we can't really even say if it's just more elders in the animal kingdom making themselves useful. Which, again, is happening after reproduction typically.
For something to have an effect on reproduction, I would think it would need to be part of the decision beforehand.