Taking it well past 80 – ie indefinite life extension, with fully automated personal healthcare (zero cost), is the only thing I am interested in.
Because in order to bring stability to how we treat each other and the environment, we all need to have a real personal interest in the long term future, and that means having a very low discount rate on future benefits (and costs).
So living a very long time in relative abundance and freedom and security gives us all a very strong incentive to treat our environment well, as we are going to have to live in it ourselves.
The down side, is that we would need to reduce family sizes on average to something close to one child (that would lead to doubling of the population – which is manageable). We cannot continue to exponentially increase the human population on this planet, and having any sort of war or pandemic or other catastrophic event increases the discount rate on future benefits and breaks stability.
So it is a stable solution to the population and environmental issues only if population on this planet does tend towards a limit, rather than towards indefinite expansion.
People who want to continue increasing population would need to leave the planet and go elsewhere in the solar system or beyond. But even there, they would run into physical limits reasonably quickly. There is only enough mass in the solar system to sustain a 3% per year growth for a couple of thousand years.
So I’m all for bite the bullet now, and create as much security, liberty and abundance as possible for all using distributed fully automated systems (which must result in exponentially expanding diversity). Providing all hold individual life as the highest value, followed by individual liberty, then the entire system does seems to be able to approach mathematical stability.