A thought for the day: nobody out there is seriously arguing for the impossibility of radical life extension, and I don't think anyone has been for quite some time. It is a given in the present diffuse discussion on the future of medicine and human longevity that at some point advances in biotechnology and nanotechnology will lead to greatly extended lives: centuries and longer lived in good health and vigor. Aging will be brought under control by medicine, like any number of other once intractable medical conditions.
It wasn't always this way. People in past centuries might have hoped for the plausibility of radical life extension, but couldn't have said in certainty that it was possible. We, on the other hand, know far more about physics, chemistry, and biology: we know that there is no wall created by the way the universe works standing in our way. The only reason we presently age and suffer is because we haven't yet advanced far enough down the path of biotechnology that is clearly visible and well understood. Aging is, at root, a matter of atoms and molecules in the wrong place and the wrong configuration. Moving atoms and molecules around to order, en masse, and with precision, is a task that we know is possible. We do it all the time, and are learning ever greater finesse with each passing decade.
Yesterday the tools were found molecules that happened to do something useful with other molecules. Today we make use of designed molecules for particular operations, knowing much more about the molecular machinery of our cells. Tomorrow the biotechnologists will build and repair complex molecular machinery that performs far more effectively than our evolved biology.
Thus discussions on the engineering of human longevity focus on how, when, and (sadly) whether it should be done at all. I see great strategic importance in the right groups gaining ground in the "how" discussion - we're all going to age to death just like our ancestors if the scientific community remains focused on metabolic manipulation to slow damage accumulation rather than the repair of damage exemplified by SENS, for example. Similarly if there are not good inroads made in growing the community of researchers interested in SENS and related lines of research.
Discussions on "when" can probably be skipped as lacking rigor: no-one knows. All the meaningful timelines depend greatly on seeds sown now that will only bear fruit in the 2030s - the course of twenty years remains a matter of long term planning and great uncertainty in specific outcomes while we're stuck living lives that top out at a century (and that with great luck). The beginnings of a larger research community, the outcome of the debate over strategy in longevity research, and so forth. It is interesting to ponder and plot the windings of future events, but that time is probably better spent on influencing the "how" discussion or materially contributing to progress.
As to the discussion on whether engineering longevity is desirable, or should be blocked by people in power - I think it never hurts to take a little time to oppose such lines of thought. Unthought opposition to extending human life or even simply intervening in the disease of aging is widespread, and success in building the research communities and funding institutions of the next few decades depends on a certain degree of broad public support.
But all that said, no-one out there is seriously arguing that radical life extension is impossible.