They lived pretty long actually. If a man survived to be 21 (therefore survived childhood illness, violence, etc) his life expectancy was 62-70 years. Which is incredible given lack of modern medicine.
Most of the low numbers are statical averages that include people dying due to childhood illness or war, and often include the bubonic plague age of death.
The life expectancy statistics are heavily skewed by child deaths due to poor medicine and hygiene. If you managed to survive to adulthood there was a pretty good chance you’d make it to old age. People definitely lived till their late 60s and longer in ancient times.
Current life expectancy may be higher, but even with modern medicine, access to food, etc. I wouldn’t say that most of the modern world is experiencing higher quality lifespan due to messed up metabolic states
IF seems to be one of many health practices that can prolong and increase healthspan, given good nutrition, etc.
Not an expert, but I’ve read a lot about medieval life, and I don’t recall seeing anything that would lead me to believe that they fasted ‘almost every other day’. If you were an average person in peacetime, you had access to food. If you were unfortunate enough to be in an area of warfare, you would be lucky to find whatever and you would eat it before somebody took it from you.
When people cite life expectancy of people back then being like 40 years or whatever they are massively skewed due to infant mortality rate, the fact is if you made it to adulthood and you didn’t catch the plague or some other deadly disease for which there was no medicine you could expect to live into your 70s…