No they really didn't.
This is what the age pyramid looks like for a first world nation: https://www.populationpyramid.net/finland/2022/
It's a column until you reach 70 then people start dying.
This is what the age pyramid looks like for a society stuck in the Malthusian trap: https://1.bp.blogspot.com/-XfdbjKDGvT0/Ti49-5r5EyI/AAAAAAAAB...
Notice how people have a half life, the chance of dying when you reach 20 years in any year is 5% regardless of age.