Redundancy is not error checking. The "error correction" mechanisms are actually just "proofreading" mechanisms and are almost entirely local and centered around transcription. Common mode errors are harder to induce due to the plain redundancy of DNA pairs but also not impossible, and once induced, are impossible to locally notice or correct. In some cases the "error correction" machinery is the cause of these induced errors. The result is genetic disease and/or cancer and is a case of missing error _checking_. Perhaps my definition was exceptionally parsimonious.

> with no medical care [...] something no computer or man made complex machine comes close to.

That's because we get far more units of "work" out of our machines than the person living for 70 years with "no medical care." Some people live just 30 years with no medical care too. And the machine does not need to sleep. We eat food they eat lubrication oil. I don't think this was a good analogy.

> it's still mostly a total mystery why we aren't immortal

While we haven't pinpointed the mechanism, we have a pretty good idea of why, and where in the system we should be looking for the answers.

> but for some reason get worse and worse at doing so over time.

You are a living Ship of Theseus and these "error correction" mechanisms are not perfect. Aside from this there are known genetic disorders which alter the rate at which people age. This is not nearly as mysterious as you're making it out to be.

> there are many animals that live ~4x human lifespans

And what are their resting respiration rates?

> and at least one species of jellyfish that is biologically immortal.

In theory. We haven't found an immortal one yet. They all die. They're also nowhere near our level of biological complexity or capability.

> Redundancy is not error checking

Yes, you are right that DNA repair mechanisms are not technically error correction in the sense that the term is used in computer memory and storage, where any isolated error is mathematically guaranteed to be correctable. You clearly have a bio background, but my intent was to point out in a simplified way to non-bio people that biological systems do have mechanisms to deal with errors. I incorrectly assumed that you didn't have a bio background, and I can see that my message would have seemed a bit condescending- my apologies.

> While we haven't pinpointed the mechanism, we have a pretty good idea of why

I study metabolism and have observed things that aren’t compatible with any of the leading theories- which I suspect are all dead ends. We are definitely missing something big still. In particular, I feel like the big anti-aging startups are throwing good money after bad, by massively funding researchers with mostly played out dead end ideas. Tech billionaires funding this stuff are re-playing the same scenario as the ancient Chinese emperors and their mercury based elixirs of immortality in modern times IMO.