The sort of question for yourself to take away from this is "what does 'natural lifespan' mean?" Obviously it has been a long time since humans have experience

The sort of question for yourself to take away from this is "what does 'natural lifespan' mean?" Obviously it has been a long time since humans have experienced a natural lifespan in the one rigorous no-technology definition of the term. Is maximum lifespan moving much? Hard to say. The data gets really sparse out beyond 110, where estimated mortality rates are 50%+/yr, and really sparse the further back in time you look. So it isn't unreasonable to hold the position that maximum life span is increasing, but slowly. Adult life expectancy at 60 is going up a year every decade, but there are so few people living to > 115 that you can't really say much about their statistics. Maybe that is going up too. Equally it isn't unreasonable to hold the position that transthyretin amyloid aggregation is a fairly equitable process that will absolutely kill everyone prior to 130. That it acts as a hard full stop on how far you can get with, even if you avoid everything else. (That this form of amyloid is what kills the majority of supercentenarians is the conclusion drawn from the limited autopsy data for people that old). This of course is because no currently available medical technology greatly impacts transthyretin amyloid (though Pentraxin Therapeutics completed initial human trials of a clearance therapy in 2015 - stuck in regulatory/Big Pharma hell, but it works). You can be as heavily treated with the best of medicine as you like, but that amyloid is still accumulating, and eventually it clogs your cardiovascular system and you die. If there was no transthyretin amyloid in the picture, I'd wager we'd have 120yr-olds in the same way that we have 110yr-olds today - a larger number of them, but still small. We'd also have 10-20% less heart disease at all ages, and a range of other conditions that are caused in old people by this form of amyloid. Amyloid clearance is a good thing, there should be more support for it.