There are real drawbacks to living in an oxidizing atmosphere. You rust. That's aging in a nutshell - the stuff that makes you work bleaches in the sun. As soon as we committed to hemoglobin we committed to an expiration date and I'm unaware of any critter that's gotten around that.

We'll live longer, presuming we maintain our standard of living. When the Soviet Union fell the life expectancy of adult males plummeted 23 years; it has yet to climb all the way back up. So much of our time is dependent on externalities.

From my understanding, one of the main things that bites you in the ass is telomeres. Forgive me if I fuck this up, but they're basically "heat shielding" - they keep the important stuff from getting screwed up by absorbing the damage themselves. As a consequence, they shorten as you age. That's what fucked Dolly the Sheep - she was born with the same length telomeres as her adult donor, which means she was "born" adult.

(Accelerated decrepitude!)

Yeah, the patching will get better. But old people die of being old. Immune systems aren't as robust. Wounds heal more slowly. Organs function less efficiently. And I'm not seeing stem cell bits being perfect replacements ever.

the NIH did a study a couple decades back where they eliminated all causes of death and did a regression to see what the average lifespan would be. I think it was like 114. That's a long-ass time when you consider it was barely 40 a hundred years ago but it's a far cry from Methuselah.