TL;DR
Every legend of a fountain of youth promised one sip. Real life looks more like a garage full of parts, and for the first time, every part is on the shelf. A therapy built to turn old cells young has been injected into human eyes and cleared for a dose three times higher. Cheap pills that clear aging "zombie" cells reversed liver scarring in a placebo-controlled trial. A compound restarted the immune system's training organ in old mice. Drugs are sparing muscle, building bone and coaxing hair back. Pig kidneys are carrying people to human transplants, and a kidney frozen for a year was thawed and made urine. One-time gene edits are holding for a year, aging clocks are being put to the test, and the FDA has started describing what an anti-aging drug would have to prove. Nobody has bolted the parts together yet. Our odds that a combined treatment reverses aging in a controlled human trial: 60%, likely by 2043. To read the odds that these parts reverse human aging and a timeline of how they could come together, subscribe.
Below the line, for paid subscribers: all eight parts with their odds, our step-by-step speculation on how they snap together, the odds for the whole machine and its bottleneck, what would change those odds, and who's most likely to build it.