Life expectancy was probably in the late 30s to early 40s during this time so you’re basically working for the rest of your life.
Death of the mother in childbirth ( 1 in 10) Death as a child because of unsafe surroundings Death as a child because of childlabour Death because of infectious wounds Death because of plagues and sickness Death because of random violence Death because of war Death by famine Death by accidents like fire in the house, occupational hazzard or hunting. Or the sinking of a ship.
All these things lower Life expectancy. But with luck and a good physique many of them could be avoided.
No, it's a myth, or even better, a common misconception. A fable is a morality story.