At that point you are getting into some of the same reward dynamics that you see with honesty in intra-species signaling. Particularly that an organism in a population may wish to signal honestly even if it knows it is unfit so that the overall population health can improve. From what I recall, many evolutionary biologists disliked the hypothesis, instead preferring the costly signaling theory as an explanation of why signals remain honest.

https://en.wikipedia.org/wiki/Signalling_theory

That assumes that the species is not smarter than nature at assessing what is "more fit" for them. For example, smart chicken that wanted to go to alpha centauri might engineer themselves to live much longer in a way that nature never would.

I'm not an evolutionary biologist, but why wouldn't the selection pressure be related to the speed at which offspring are produced, and not the age of the parent? And why wouldn't a parent that lives a long time and thus produces more offspring be evolutionarily fit?

There are a lot of factors involved in having viable offspring. For example, you need enough resources to sufficiently feed and nurture the children you already have. So having more offspring than some ideal amount for the environment can be detrimental. But parents also compete with their offspring for resources. Aging and dying is eventually the best thing a parent can do for their children.

This doesn't really work at the individual level. Parents compete with their children, but so does everybody else. Having two parents competing with you for resources in addition to the other ten thousand people in your local community is not a meaningful difference.

Meanwhile if there was an entire community like this then the people living longer still wouldn't be at a disadvantage, the community would just have a different equilibrium. The surviving communities could e.g. have fewer children on average (you only have to replace people who die in accidents) or would expand their territory over time (expanding population can control more territory).

That's a fair point about competing with the community. I was thinking of "parents" in aggregate, so the previous generation vs the next, but I didn't word it right.

But if everyone lived longer than required, i.e. the minimum ideal for raising viable offspring, then this population stood to be out-competed by another population that aged at a more efficient rate. Individuals in a population aging at an optimal rate is an evolutionary advantage to the population.

This might explain why genes for aging exist but doesn't really explain why genes for not aging don't exist. You could have a stable community where e.g. 15% of the population doesn't age and not run into community-level problems because they aren't that large of a percentage of the community, so where are they?

Hard to say. At least in the case of humans, high generational turnover might have been beneficial in our evolution from aquatic apes or whatever our ancestors were to modern humans. And so longevity genes were selected against. It might be the case that most species' environments are too dynamic for super longevity genes to be beneficial rather than faster population adaptation.

The older you get the more difficult it is to conceive children as well as raise them. Given that most people have a partner that is roughly the same age as them, and that there would be a much smaller percentage chance of pairing with someone with the same long life trait, the period of time that they are likely to have children probably stays consistent with societal norms. Therefore living a long life wouldn't increase the number of offspring and wouldn't provide any evnolutionary benefit.

> The older you get the more difficult it is to conceive children as well as raise them.

Are you trying to provide an evolutionary justification for aging by using aging itself as a reason?

So then, once a population reaches "ideal" mutations, if that is possible, then wouldn't the opposite start happening?

There is no static ideal. The total environment is incessantly changing, and organisms are constantly adapting.