The thing is, we don't know really. Is aging evolved, or a disease? Or a complex of some evolved and some diseased mechanisms interacting... Or something else.. i don't think we know yet for sure.
We know, you can see it under a microscope. Take the simplest living structure, you'll see it will break down over time. Then go progressively bigger - you'll see the organism is doing work to keep itself together and well. These mechanisms are increasingly complex with scale, and not designed with that (or any other) purpose in mind, that makes it extremely convoluted and sometimes even counter-productive. The problem (from our point of view) is that there is no reason to keep doing this work after we procreate, that caused us to evolve workarounds instead of solutions (e.g. telomeres long enough for few decades, but not more).
actually I don't think that's what you'll see in a given time. I think if you take the tiniest living organism and look at it under a microscope you won't see it breaking down over time you'll see it reproducing or eating or moving around. I think it does those things with greater frequency and on shorter time scales then it breaks down. And I'm pretty sure there are some tiny organisms that you know don't break down at all.
But I'm not denying that breaking down and entropy is an almost universal fact of life for most of life.
and I agree that from an evolutionary perspective there's no point repairing the body after the sort of population average procreation age. and in fact I think someone else mentioned in this thread that you know there's some organisms that die immediately after procreating. And I'm also not disputing that repair mechanisms and things like telomeres have a genetic origin... that seems obvious.
However this sort of decay behavior and repair behavior is not universal there are some things that are a lot more durable but even if we assume that it's universal, i don't think you can tell or I can tell whether, nor the extent to which, decay is a disease or genetically evolved solution to some problem that we don't understand yet, or some complex interaction of the two.
The possibilities of some of the potential consequences of immortality have been discussed in this thread and people have proposed aging as a genetic solution to that, and an explanation for why agelessness which, on the face of it seems like it would be adaptive, has not evolved. So I honestly don't think we know the degree to which aging or agelessness is genetic or is diseased, or a complex of both. And I don't think your relatively simple, but still on some level convincing, example establishes that either way.
