Making predictions is hard, as the joke goes, and especially when they involve the future. That said, predicting very broad trends and general capabilities in technology seems to be somewhat tractable if you go about it in the right way, such as by researching carefully and restricting your predictions to the future capabilities of fields that present have a solid research community: large, well funded, and well supported. Even so, making specific predictions as to how future capabilities will be used is a fool's game.
I would say that the principal cause of uncertainty for the timeline leading to rejuvenation biotechnology - ways to repair and reverse the cellular and molecular damage that causes aging - is the fact that we lack a large, well-funded, well-supported research community at this time. Only comparatively small initiatives exist now, such as the SENS Foundation, and the actions, choices, and happenstance of individuals have large effects on the future timeline leading to the desired solid research community. That future community will be large enough that individual choices don't tend to have much of an effect on its progress one way or another, but here and now the element of chance is significant.
So it is much easier to look at, say, the regenerative medicine research community and make solid, well-thought predictions as to when we'll see limbs and organs regrown. Similar, one can plant flags on the field for rejuvenation biotechnology if we restrict ourselves to talking about how long things might take after large numbers of dollars, supporters, and willing scientists arrive on the scence. That's thought to be ten to twenty years and one to two billion dollars to rejuvenate old mice if you're looking at the SENS plan. But how long until the necessary dollars, supporters, and willing scientists arrive? How long is a piece of string? The bootstrapping process of persuasion and fundraising goes as rapidly as it can be made to go.
Another field of longevity science is the business of understanding and manipulating metabolism to modestly slow aging - so as to perhaps one or more of the beneficial mechanisms of calorie restriction through a drug, for example. This area of research has grown to a solid research community over the past decade: we can make reasonable predictions as to how long it might take them to show meaningful results. Unfortunately, those results won't be very helpful in the grand scheme of things; likely a few years of additional life at most for those of us who will be old by the time those products make it out of the gate, and that will have been bought at a cost of decades and billions of dollars that might have gone towards more useful work. I'm not belittling the usefulness of basic knowledge of metabolism, just the tendency to treat that as the only way forward for extending healthy life, when clearly a far better option exists.
Still, in terms of the way in which the broader public look at longevity and science, we're a long way ahead in comparison to the state of affairs back in 1990 or 2000. One of the reasons that metabolic manipulation has been able to grow into a solid field is that a great many people are starting to take it as a given that life span is increasing, albeit modestly, and that medical progress means longer lives are in the offing. That's a better starting point for new advocacy than has been the case even in the recent past. One source of this new understanding is, interestingly, the massively capitalized pensions and insurance industry: they have a loud voice, and the financial markets are an important source of news and knowledge in our culture. There are whole segments of the population who sit up and take notice when rumblings about longevity emerge from those sources rather than from scientific publications. For example:
The failure to consider future drivers of mortality in historical predictions has "contributed to employer pension funds under reserving for longevity risk and other bodies, including governments, not budgeting effectively for funding an aging population", said Daniel Ryan, head of life and health research and development at Swiss Re. The report calls on medical experts, actuaries and demographers to work together toward a greater understanding of potential future developments in human longevity.
The level of uncertainty in developments that will extend human life is making the big money in pensions, annuities, and the like uncomfortable, and has been for years now. That is, more or less, a vote of confidence in the scientific community, or at least a vote of confidence in what is possible and how likely it is thought to come to pass. Yet we're still at present stuck without a solid research and development community for rejuvenation biotechnology, something that would make the future a great deal more predictable. Helping to create that community is the first job on the list until such time as it is accomplished.