My mother-in-law was born in 1931 but my generation does not have to wait until her death to begin.
If you think a generation is 40 years you come up with between 4651 years and 5051 years.
You cant find a scholar that believes that its been less then 6000 years since creation. Also, I cant find a scholar that believes the earth is over 7000 years since Adam.
There are disputes among scholars as to the exact generations from Adam to Jesus but by all accounts it is somewhere between 6 and 76. I personally believe it is closer to the 66 number then the 76 number.
All considerations taken into account the 70 year generation has to be closer to scriptural truth then any other much shorter number.