TL;DR
Researchers in China fed old mice, about 18 months old (roughly the human equivalent of the mid-50s to 60s), a compound that blocks a single enzyme whose activity climbs with age. The treated mice lived an average of 28 months instead of 24, about 17% longer, and they did not just last longer: they were less frail, ran and hung on better in strength tests, and remembered better. For people, the hope is a drug that could be started in late middle age and buy both extra years and better ones. The result so far is in mice, from secondary coverage, and the next step is a first trial in people. To see our odds on when a drug like this could reach a first human trial, and the timeline of breakthroughs that leads there, subscribe.
Below the line, for paid subscribers: The full story: where it stands, how we got here and what's dated next; our labeled speculation on what it adds up to; and every source.