There's one popular misconception that everyone died young in Ye Olde Times of Yore. As you note, Michelangelo and some other historic persons with documented lives refute this misconception.
It's also incorrect to attribute shorter historical life expectancy only to infant mortality. That's why I replied to the post by mullingitover. In 1900 Americans had barely even odds of living to age 60 once they had already survived to age 18. Again referencing the Social Security data I originally linked, life expectancy at age 18 increased by 17.3 years (60.3 to 77.6 years), or 29%, over the course of the 20th century.
The maximum life spans documented among the very oldest people are also interesting, and show much smaller gains, but are separate from questions of average life expectancy among infants, children, or young adults.
“Maximum lifespan is believed to be under genetic control”
Given modern medicine etc. more people are approaching the maximum lifespan, but we aren’t increasing the maximum.
Some people in the middle ages lived well into their 80s, just not nearly as many as today.
For example, 600 years ago Michelangelo lived to be 88. https://en.m.wikipedia.org/wiki/Michelangelo