When doing the calculations be sure to QA your LYs. Spending an extra week lying doped up and in pain in a hospital bed may not be worth all that much. Also with medical research, you often wind up with a patented drug which then costs $1e5 per patient treated at least for the first decade or two of its use at least as used in the USA and other non-single payer countries. Or it requires $1e5 of medical professional intervention per patient to implement. My priors are that the low-hanging fruit is not in turning 90 year olds into 91 year olds, and won't be for many decades.