No it doesn't. If you have 100 people of which 50 died below age 10 and the 50 that survived lived to 75 that's a lot of retirees. If all 100 survive past age

No it doesn't. If you have 100 people of which 50 died below age 10 and the 50 that survived lived to 75 that's a lot of retirees. If all 100 survive past age 10 but 90 of them die before age 65 you have not a lot of retirees. The exact numbers can work out to the same "life expectancy" with wildly different results for retirement planning. And also in genealogy the high infant mortality rate makes for small average life expectancies and you might be surprised how old most people that survived to adulthood actually got.