The largest single one that I can identify is healthcare. A conservative measurement of end-of-life care makes it 13% of healthcare costs, and if healthcare is 17.9% of GDP in the US that is means we save (0.13 * 0.179 = 0.02327) ~2.3% of GDP for as long as those expenses can be deferred. This does not include treatment of chronic conditions or other risks which are made worse by senescence (falls, Alzheimer's, etc).

This will depend on details, such as: if you double someone's lifespan, have you effectively increased their middle age, or their old age?

If it's all middle age, then it will be in the interest of our overlords to make us live longer, so that we can be longer productive. The salaries would probably go down, because now you have more time to pay your mortgage (and you are competing on the market with other people who also have more time to pay their mortgages). Also, no one is impressed with your 30 years of experience in given industry, because that's an average among your competitors.

Education will take longer, because other people will signal their qualities by taking more loans (they now have more time to pay back) and staying at school longer. Mere PhD will only get you a job flipping hamburgers at McDonald.

Death of society's "old guard" may be serving a useful purpose by destroying calcified institutions and ideas, allowing better ones to bloom.

Somehow I expect this reasoning will only be applied selectively to the poor. (Yes, that includes the middle class.)

In summary, I expect the society will support those forms of anti-aging that prolong the productive years. Which is not bad, because that means more years with health. Just don't expect that you will be the one who benefits most from your longer life; you will spend most of the extra time in the workplace, working more and receiving less. Enjoy your college, though, those will be the best 30 years of your life!

[Epistemological Status: I remember hearing all of these things but I could be wrong about a bunch of them. Take this more as my intuition than as a fact]

Right now, the age distribution of a given country is considered to be a very important factor in its economic development. This is because

• Elderly people are less likely to make major (retail) purchases before they've already accumulated the things they neeed over the course of their lives
• Elderly people are less likely to engage in professions because
• They are more likely to have enough wealth that working is unnecessary
• One's age often inhibits professional capabilities
• Elderly people are more likely to require familial support from their children and grandchildren; putting strain on their ability to work or their level of productivity while working

A lot of the economic strains noted above correspond to either the effects of aging or the economic situation of the elderly. Of the two of these, I think the effects of aging are much more important. While aging is a biological reality, things like the desire to continue working after being alive for a long time can change with culture (and even now, I know many elderly people who would like to continue working).

For this reason, I think anti-aging treatments targeting effects of aging rather than life extension are likely to be an overall economic benefit. It will give the elderly who want to work but can't because of health reasons the opportunity to do so. The result may be a larger workforce and higher consumption (even if that consumption is focused around getting toys for the grandkids).

Similarly, anti-aging treatments that prolong old-age will probably increase economic strain in terms medical costs and familial demand.

There are also other potential benefits to longer healthy lives:

• If people have more time alive, they have more slack to take risks and try things that they're interested in
• Academic problems that demand an unusually large time investment to fully understand may be tractable. No idea whether these actually exist or not but Scott Alexander wrote a cool story about it. Progress may get faster
• People care about their own welfare so people who live longer may care about worldly conditions over a longer time-frame than they did previously. This could make people think slightly more long-term about their decisions

But how does this compare to just having more kids?

You mention that raising a kid costs $234K. But adults, even frugal ones, may have around $25K annual expenses. This implies that keeping an adult around for the same amount of time (17 years) costs upwards of $425K. This would be more resource intensive if those adults were not working. If we account for the fact that adults pay their own expenses and kids don't, funding adults life-years strikes me as more economical than paying for more kids. The implication here is that, not only do adults demand fewer resources than kids but they also contribute more to the economy (in spending) than them.

So, overall, I'd guess that life-extension would be an economic benefit. However a lot of these factors are very culturally dependent and the ways that life-extension would affect culture could vary.

There is no proved working antiaging technologies. Some possible interventions are relatively cheap, e.g. metfomin bulk cost is few dollars for kg, but they could provide at best 1-3 years of life expectancy.

Given the exponential decline of the price of any new tech, future anti-aging tech (e.g. nanobots-based vaccine against aging) will be as cheap as a new smartphone eventually. For example, other current life-saving drugs are also very cheap now: vitamins, vaccines, antibiotics.

Thus saving life will be cheaper than rising a new person (at least until mind uploading when copying will be cheaper).

Well, what about the psychological side of things?

Could humans take even more (obligatory) education time? Even more time working? We are already seeing the bad economic impact of an older retired population that's being sustained by welfate and their own savings in some europeans countries. (see Portugal)

If society opted for longer productive life spans, it would come with a need to control population growth even harder, else t

This is a great question because it leads to so many other interesting ideas. I think if such a discovery was made then a good majority of our societal constructs would have to be restructured. You expressed is quite well with your point on economic losses. I do believe it would level out and we would find more gains than losses; but it would require a substantial change in how we operate.

inter-society competition will not particularly favor anti-aging investment

• While life-extension may very well be outcompeted (in particular, birth rate changes the exponential base while life-extension only adds a constant factor), this particular failure mode seems wrong because group selectionism doesn't work
• Don't even worry about it, unless the future is ruled by a Singleton, Moloch will win anyway, by default, in more ways than we can imagine

Relevant book: https://www.juvenescence-book.com