That’s an interesting question- some genealogists consider 25 years to be one generation, but I believe that it should be 33 and 1/3 years. I think that my number is closer to the average generation. I believe that it is the approximate midpoint of a woman’s normal childbearing span, from young 20’s to mid 40’s. And yes, I’m perfectly aware that childbirth is possible at a younger age.
.
One generation is the average age at which a newly married couple begins their next generation.
In Isaac’s time it was 14 years, but now its more like 21 or so.
.
25 years is closer to the historic midpoint. Women who looked fertile were usually first pregnant in their early teens. 20 was considered old for a first child until the 20th century.