In many cities you can see that the lifespan increases with the average household income of the neighbourhood, and if you look at say, Monaco, one of the richest per-capita cities, the average life expectancy is 85 for men and 93 for women, over 20 years longer than the average European scholar.
Modern medicine helps to extend life expectancy but often those last 10+ years are miserable clinging to life whereas in the past once you got, for example, a chronic heart disease you would not survive very long. The healthy life expectancy in the past can only be a guess but probably not that considerably lower for certain classes.
An intentionally simple example of how dramatic it is:
Ten people, with 20% of them dying in childhood. Then reduce that to just one dying in childhood.
80, 75, 70, 65, 65, 60, 50, 40, 2, 1 = 50.8 avg
Now drop the childhood deaths down to just one.
80, 75, 70, 65, 65, 60, 60, 50, 40, 1 = 56.6
You gained 5.8 years on life expectancy from cutting the rate in half. Now take us from 1650 childhood mortality rates, to affluent modern nations where it's eg 5 deaths per 1000 live births in a nation like Canada (and that's down by 75% from 20 per 1000, 50 years ago). I can only imagine how high the rate was 400 years ago, it would absolutely tank the average in an epic way.
Bill Gates for example routinely claims in interviews / discussions that there has been a massive gain in life expectancy (technically correct) and he'll claim that broadly (mostly false), dropping context on the fact that it's heavily caused by childhood mortality figures plunging. I've seen him do that numerous times over the years (usually he gets agitated when someone challenges him, moves into sarcastic mode, and points out the huge gains for the average person on life expectancy, which is partially bunk). It's a common point of intellectual dishonesty in the scientific & health establishment, because they want to pretend the life expectancy gains for adults have been far greater than they really have been (for their own self-interested reasons). I suspected the parent comment was riffing on that aspect, where it's a pushed point of quasi propaganda that life expectancy has soared for everyone.