The days of our years are threescore years and ten; and if by reason of strength they be fourscore years, yet is their strength labour and sorrow; for it is soon cut off, and we fly away. Psalms 90:10
That’s 70-80 years, not 40.
70-80 years is mentioned as a lifetime, not a generation. A generation would seem to be in the range of twenty five years or so, the average age of the father of an average (or median) child.
Good scripture reference, and is there not also another saying we are limited to 120 years life expectancy? So with all the medical advancements I’d say we could easily wait up to another 50 years.