If 70% of 18 year olds make it to 40, then so long as 5/7 of them can survive another 20ish years, you have “most” people making it to 60. If we’re cool with a +/- 5 years on the “about 60” figure I think this tracks just fine.

Nevertheless, that was the 18th century in industrializing Britain, which was becoming a lot more efficient at agriculture etc. From many aspects, it was already a fairly modern society, with an emerging literate middle class etc.

Even then the mortality was still quite high compared to today.

And most agricultural societies before that were regularly swept by famines, which disproportionately took the young and the aging ones.

When judging historic lifespans, we tend to judge by the famous people. Cardinals, popes, kings, emperors. The population average was way, way lower, and the bones from churchyards tell the real story.

I’m judging by just glossing through some tables of data.

The median death for 25 year olds was about 58 in Ancient Rome for example

Surviving death records from Ancient Rome are far from representative. Contemporary record keepers were mostly interested in heads of households, and not, say, slaves. So this again skews the statistics towards richer and more influential people.

Also, Rome itself (as a city) had never problem supplying its population with food. There was a special office (Cura Annonae) that coordinated import of food from Hispania, Africa and Egypt to Rome so that the city was never threatened with starvation. I just recently visited Ostia Antica, the main port of Ancient Rome; it was absolutely massive. Rome certainly had a lot of problems, but it was fairly secure in food.

Things were different in 11th century Germany or Sweden. Without an extensive network of long-distance trade, if crop failed in your region, there wasn't any way to prevent famine.

Even deep in the 18th century, during the last peacetime famine in Czechia (1770-3 approx., caused by rainy and cold weather), the attempts to alleviate the hunger by importing food from Hungary were only partly successful; even though by that time, the road network was fairly developed and the state capacity was orders of magnitude higher than several centuries ago. As a result, something between 5 and 10 per cent of the population died.

Can you find some data to support your claim? Ideally one not cherry picked to a known famine/plague/war?

This was likely due to the population density and sanitation conditions of city living causing infectious disease related deaths, no?

I imagine the risk of contracting fatal diseases in a rural setting was much less.

Crop failures were a major factor in mortality. Subsistence grain farmers in pre-modern times could expect a crop failure once in 5-7 years, sometimes back to back.