The life expectancy for a 1-year old has gone something along the line of +40%. That's significant but not doubled. Infant mortality is by very large margin the most important factor in the changes to life expectancy at birth. And you can get most of the way there with just basic hygiene rules. Full on modern medicine only helps with the hedge cases.

One interesting data point is that the age at which people transition economically from accumulating wealth to transferring it has remained about the same (around 64), at least as far as Western European inheritance records prior to demographic transition show. Ie. people retire at the same age. They just spend more time being old. I'm not sure it's all that much progress. I wish we found ways of making people useful longer, rather than just trying to keep them from dying.

The interesting number isn't average lifespan though, it's average lifespan after you reach 20.

> The modern Amish also don't currently live in a society with endemic smallpox.

That's why I said access to doctors, not to public health, which is what's kept most of us alive. Though I don't know how modern their approach to childbirth is, that one's important.

If you don't die from an injury or disease, humans lived about as long as they do today. It's under 5 year old mortality, childbirth and disease and injury that made us die more on average which reduced our life expectancy.

This means that our actual durability and lifespan hasn't improved that much, just our ability to fix and avoid previously fatal injuries.

If humans weren't genetically encoded to die from old age, vs just plain wear and tear like you would with a car, you would statistically see a small amount of humans who lived until 300 today. Just like how there are thousand year old well preserved physical objects today.