Today we stand at least 20 years from the first comprehensive suite of effective therapies to either slow aging or reverse aging, even in the best of plausible scenarios – although some parts of that suite will likely emerge sooner, such as senescent cell clearance. Many of us will be old by that time: methods of slowing aging that work by reducing the pace at which damage accumulates will do very little for someone who is already aged and very damaged. A therapy that can even partially reverse aging by repairing the damage that causes degeneration will be far more beneficial to old people. Further, a therapy that repairs damage can be used over and again as damage reoccurs with the passage of time, and will provide a benefit each time it is used. Drugs that slow aging would have to be taken on an ongoing basis, producing only a small short-lasting benefit with each dose, and the end result is still that an individual will age to death. In comparison, a set of sufficiently effective repair therapies could be undertaken once every few years to indefinitely hold off the progression of aging.
The differences in utility are very clear. So if billions of dollars and decades of time are to be spent on developing either a way to slow aging or a way to reverse aging, why not work on the obviously better solution rather than the obviously worse solution, given that the costs are in the same ballpark? The real threat to our future that I see today is that the bulk of funding and present work on human longevity is focused on drug discovery to slow aging – research that will likely result in little to no benefit for anyone entering middle age today. If you and I want to live longer, healthier lives, then work on rejuvenation must instead become the priority.