I suspect many people in old age really want to live, they just don't want to live in old age. Meaning if they had the opportunity to become 20 again most of them would take it.

I honestly suspect the simulated biology in combination with delivery tools made from synthetic biology (aka artificially programmed cells) which can delivery nearly any kind of package including CRISPR, drugs, etc... to a specific cellular target (even down to the behavior of specific cell types) anywhere and/or everywhere in the body. We're developing that kind of synthetic biology already, and in some cased like Car T Cells its already in use and has been proven to be extremely effective. We're currently working on making it a lot cheaper. With those tools and a fully understood genome, bioelectrical signaling, and epigenome we would be able to do nearly anything and be masters of biology to the point of potentially being able to design and grow new types of body parts and organs or add new features to those that already exist in living people. First we'll be able to do things like grow a tail or horns though or adjust body proportions (no more plastic surgery).