Living Long
People in the Known World stay vigorous far longer than the world has any explanation for. Most remain strong, clear-headed, and capable well into their seventies and eighties; visible decline arrives in the last decade or two rather than the last four. A healthy person of seventy has the stamina and the skin of someone twenty years younger by any standard our world would recognize. A great many live actively into their nineties and some past a hundred, and then fall away fairly quickly at the end.
The world attributes this to clean living — better food, better water, precise medicine, disciplined self-care. It is a reasonable explanation, partly true, and nowhere near sufficient. Every one of those things helps and none of them adds twenty years. Nobody has noticed, because there is no population without it to compare against.