Engineering might be regarded as the process of production of working technology in the absence of complete knowledge - the strategies for managing the unknown, and applying what we do know with rigor and to good effect. Bridge building and large-scale construction came to a fair and effective maturity long before the scientific, mathematical and computation tools that enabled rigorous models and full understanding of the underlying principles, for example. So too with medicine: it is an engineering discipline aiming for the best possible results with the information we have right now.
More information is better - bridge building was greatly improved through the development of those mathematical and computational tools - but we don't need to know everything to make significant progress. We just need to know enough; I think that the history of medicine to date amply demonstrates that maxim. You can find the argument that we know enough now, today, to make significant progress in repairing the damage of aging at the Strategies for Engineered Negligible Senescence section of the Methuselah Foundation website, and the details backing up that argument in the book Ending Aging.
The short of it: aging is the consequences of an accumulation of a small number of different types of cellular and molecular damage throughout the body. Scientists know what those forms of damage are, and have good ideas as to how to proceed with repair or removal. In some cases, that repair has already been demonstrated in the laboratory.
The biggest problem I see today for the future of longevity science is that the bulk of the aging and longevity research and development community is not focused on goals in medicine and engineering near-term therapies of rejuvenation. There is no urgency and directed purpose analogous to that in the cancer research and development commmunity. The community is instead mostly focused on observation and complete understanding of biochemical changes with aging. This state of affairs is much as if we lived beside a great chasm, but instead of engineering bridges for the benefit of all, we held off any such work until the full modern science and understanding of architecture was developed. Waiting too long has costs. In longevity science, waiting is measured in millions of lives lost with each passing month.
Here's a good example of the sort of productive research that takes place in the mainstream of aging science:
The major cell signaling pathways, and their specific mechanisms of transduction, have been a subject of investigation for many years. As our understanding of these pathways advances, we find that they are evolutionarily well-conserved not only individually, but also at the level of their crosstalk and signal integration.
Productive interactions within the key signal transduction networks determine success in embryonic organogenesis, and postnatal tissue repair throughout adulthood. However, aside from clues revealed through examining age-related degenerative diseases, much remains uncertain about imbalances within these pathways during normal aging.
Further, little is known about the molecular mechanisms by which alterations in the major cell signal transduction networks cause age-related pathologies. The aim of this review is to describe the complex interplay between the Notch, TGFbeta, WNT, RTK-Ras and Hh signaling pathways, with a specific focus on the changes introduced within these networks by the aging process, and those typical of age-associated human pathologies.
Is this important and useful? Yes, of course, very much so. Is this knowledge necessary for us to proceed to reverse and repair aging? No. We already know what the damage of aging is, at the cellular and molecular level. Knowing more about the way in which that damage twists our metabolism and controlling biochemistry will help, in the same way that modern techniques of architecture improve bridge building, but the absence of that knowledge does not hold back significant advances in the engineering of healthy longevity.
The only present barriers hindering rapid and aggressive progress towards rejuvenation of the aged are those of will and funding. That is why we can all help to make a difference to the future of aging science - you don't have to be a scientist to help make will and funding a reality.