> If we had 10 times more time to live, we wouldn‘t necessarily be getting ten times more out of it.
We would probably need to work 10 times longer, because everything would be more expensive. We compete for scarce resources with other people, and if we have more time and they have too, the extra time will be burned in the zero-sum competitions.
That and the human population would rapidly saturate the planet within this century. That of course may happen anyway, however as is we at least have a fighting shot at managing it. Life expectancy expansion has to be gradual so we can adjust to it (in numerous ways), otherwise it'd likely prompt a cataclysmic humanity crash (bubble then crash). Beyond things getting more expensive, we'd probably just have a plain resource-driven civilization crash in much of the world.
Annual births more or less peaked in 1988 at around 139/140 million, which is close to the level we're still at today [1]. Annual deaths however keep climbing, from roughly 48m in 1988 to 60m or so today. Births are set to decline while deaths keep climbing throughout the century.
Clear most of the natural deaths for just the next 80 years, and it's the difference between then having 18-20 billion (or more) people in the year 2100 versus the present common projections of around 11'ish billion. Would have to resolve in the fantasy age extension scenario whether people can keep having children for hundreds of years, as that would change projections radically. Governments would likely aggressively regulate population expansion if so, rather than hoping for self-restriction (eg if it took a natural form of tapering via per capita births dropping to match the changes). Does raising a child become a 100 year responsibility? Does our pre-adult immaturity / adolescence time expand to fill the allotted life expectancy? Lots of questions in the fantasy premise.
We would probably need to work 10 times longer, because everything would be more expensive. We compete for scarce resources with other people, and if we have more time and they have too, the extra time will be burned in the zero-sum competitions.