Children died, a lot. You're confusing the definition of average.

The thing is that with all of our medicine we haven't much increased the age at which people die from being old. Plenty of 75 year olds back then, but they almost all had a sibling that died of a childhood illness.

Mostly what medicine has done is vastly increased your chances of living to adulthood.

Yeah sure, but regardless, if someone told you that someone died when they were 66 years old, would you say that they died "so young"?

25 year olds don’t. 70 year olds do. We had a friend who died at 55 from health problems. Lots of “so young”s to go around.