Whatever happened to those blood transplants people were getting from younger people? Logically it made sense, but I'm guessing after further study it didn't pan out? Or was it just a trend that didn't get any follow up?
https://onlinelibrary.wiley.com/doi/10.1111/acel.70103
https://longevity.technology/news/human-trial-finds-therapeu...
There are a couple reasons to believe that aging is malleable.
One is that we know how to de-age human cells using the same factors that fertilized oocytes use to de-age the underlying egg cell (typically many decades in age). https://en.wikipedia.org/wiki/Induced_pluripotent_stem_cell
The second is that nature has examples of biological immortality. Planaria are a fascinating one as they have among the trashiest, most mutated genome on the planet. They're even polypoid, where they have multiple sets of chromosomes, but they're simultaneously the best regenerators on the planet. Despite having a discrete nervous system and centralized brain, you can slice a planaria into hundreds of pieces, and each of those will regenerate into a full, functional adult. They don't age, they don't get cancer. The issue is that we have no idea how this happens. So there is still a lot for us to learn about the fundamentals of aging and regeneration overall.
not dominant if mean life expectancy is < 40. Aging only has an impact after age 55.
(and if 55 seems young, you have a cushy life)
Two, ethics,
Three, it took something like 10K young people per old person to make it work, and it was at best a proof of concept
Four, ethics