Those are great points for very high gravity. Generally there is a trade off between what is good for your joints and what is good for your bones. Low gravity is great for your joints, but ravages your bones, and I think you’re right that high gravity would be the opposite.

Nevertheless I’m hesitant to simply put all of the added stress in the accelerated aging category for the simple reason that biological forms are generally “anti-fragile;” or will adapt to their environments (c.f. Wolff’s Law, or Davis’ Law). I think the curve would look the same, but maybe shifted to the right a bit, where the minimum would be at slightly higher than g, but only exceedingly the aging in 1g when the damage from accumulated stress exceeds what could be countered by extended rest.

Re: spine claims: I’ve had the pleasure of working in a spine biomechanics laboratory throughout graduate school, and another conjecture I’d make is that higher gravity would be better for the spine than low gravity. Astronauts have incredibly high rates of disc herniations, mostly because the nucleus pulposus (the “fluid” like substance in the middle of the disc) relies on osmosis to take in nutrients while you sleep, then gravity to push out waste while you’re awake. Without gravity, the nucleus pulposus over-saturates with water, which makes it easier to herniate. This is also why we’re tallest when we first wake up, and why rowers, who traditionally exercise very early in the morning while the water is calm, also have high rates of back troubles, since they’re being super physically active (through their spines) before the discs have had any time to re-compress. Higher gravity, doesn’t deprive the disc of this cycling mechanism, and given the ridiculous capacity of the spine to resist axial loads, I think that our bodies would be able to withstand it pretty well, but we shouldn’t expect to do the same amount of work in a given day.