I wonder how long people could live if they underwent organ and bone marrow transplants whenever necessary. If your kidneys are 85 years old and on the verge of failing, replace them with a pair from a teen who is being kept alive solely for use as an organ garden. Likewise with other body parts. Fragile bones in old age? When you break the femur on a fall, instead of waiting ages for recovery, get a replacement from a donor, or a piece of metal pipe installed. My guess is that tissue and blood vessel replacement would be the limiting factor, as I’m not aware that such replacements are possible these days. Still, I’d not be surprised if these surgeries extended a person’s life by a hundred years.