Making up numbers is not the way to do this, then.

He's not making up numbers. It's a pretty legitimate extrapolation of what the consequences would be if one could eliminate increasing mortality and maintain the mortality rates of young people. This is no more 'making up numbers' than is using e=mc^2 to point out the potential benefit of atomic energy.

If you want to introduce people to the idea that very long and healthy lives are possible and desirable, a historical perspective would be good. Or you could discuss how we lead relatively healthy lives until about 60, and then somehow the decay kicks in - which is really a shame because we've been healthy for so long, and there shouldn't be a moral reason why it can't stay this way.

Still missing the point. Nothing about the observation 'hey, being 20 years old is pretty nice' or 'decay kicks in around 60, isn't that odd' implies 'eliminating increasing mortality would result in lifespans on the order of a millennia' unless one has already taken known annual mortality rates and worked through the probabilistic implication - the very working-through you're mocking as "making up numbers". (Certainly the average Guardian reader, or the 99th percentile Guardian reader for that matter, is not an expert on gerontology and will have never realized this, and needs it to be pointed out.)

Additionally, my point is not that it's ultra-mega-hard to extend the human lifespan, and that we shouldn't even try. But we have to take into account how the system actually works, and then start from there. That is, we have to build a model, then see if we can improve the situation (i.e. extend human lifespan to 1000 years) by varying parameters within the model.

Cost-benefit. You keep talking about the costs and exact mechanistic models of aging, while ignoring the overall observation which gives an idea of the benefit.

There's a difference between this, and the original writing. You already have a good reason why the real energy content of matter should be way higher than it appears to be.

This is equally applicable to the aging, and why I chose it. 'You already have a good reason why the real upper limit on lifespan should be way higher than it appears to be, because some actual empirical mortality rates imply that we could live for a long time'.

I have a feeling that I don't understand your point or how it relates to mine, or that I don't see that you would understand my point.

I don't understand how you can fail so badly at understanding the basic argument. The logic of the article is transparent and standard among coverage of futurism & speculative tech articles: 'here is a quick estimate of how valuable such an achievement could be which will be surprising to most readers who are not already experts on how aging works, here are people who think the achievement may be feasible, here's what they and others are working on and possible routes, and here's the summing up conclusion'.

When you read the first paragraphs, what does it parse as, logically, in your mind? Can you write out a summary of the article, or does the whole thing just look like a big mish-mash of 'blah blah blah making-up-numbers blah blah blah caloric restriction blood donations Calico other-stuff-I-don't-care-about' and you get angry and decide to vent about it on LW?