Psalm 90:10 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.
Genesis 6:3 And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.
According to Wikipedia the current world average life span is 67.2 years which would seem to agree with Psalm 90.
We might reasonably suppose that the 120 years in Genesis 6 refers not to a maximum life span but to the time between God’s decision to destroy the people upon the earth and the commencement of the flood. Noah was 600 years old when the flood began and lived to be 950.
The 120 years delay in judgment demonstrated the longsuffering of God that Peter refers to:
1 Peter 3:20 Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water.
The lives of Noah’s offspring down to Abraham and Jacob were not restricted to 120 years.
Genesis 11:10 These are the generations of Shem: Shem was an hundred years old, and begat Arphaxad two years after the flood: 11 And Shem lived after he begat Arphaxad five hundred years, and begat sons and daughters. 12 And Arphaxad lived five and thirty years, and begat Salah: 13 And Arphaxad lived after he begat Salah four hundred and three years, and begat sons and daughters. 14 And Salah lived thirty years, and begat Eber: 15 And Salah lived after he begat Eber four hundred and three years, and begat sons and daughters. 16 And Eber lived four and thirty years, and begat Peleg: 17 And Eber lived after he begat Peleg four hundred and thirty years, and begat sons and daughters. 18 And Peleg lived thirty years, and begat Reu: 19 And Peleg lived after he begat Reu two hundred and nine years, and begat sons and daughters. 20 And Reu lived two and thirty years, and begat Serug: 21 And Reu lived after he begat Serug two hundred and seven years, and begat sons and daughters. 22 And Serug lived thirty years, and begat Nahor: 23 And Serug lived after he begat Nahor two hundred years, and begat sons and daughters. 24 And Nahor lived nine and twenty years, and begat Terah: 25 And Nahor lived after he begat Terah an hundred and nineteen years, and begat sons and daughters. 26 And Terah lived seventy years, and begat Abram, Nahor, and Haran.
27 Now these are the generations of Terah: Terah begat Abram, Nahor, and Haran; and Haran begat Lot... 32 And the days of Terah were two hundred and five years: and Terah died in Haran.
Genesis 25:7 And these are the days of the years of Abraham’s life which he lived, an hundred threescore and fifteen years.
Genesis 35:28 And the days of Isaac were an hundred and fourscore years.
Genesis 48:28 And Jacob lived in the land of Egypt seventeen years: so the whole age of Jacob was an hundred forty and seven years.
I do not think that the inspired word of God contradicts itself.
The point being made in Psalm 90 is not that no one lives past 80 (because it is evident that some do) but that at an average of 70 years our lives are relatively short and we should not waste our days in vain pursuits.
Psalm 90:12 So teach us to number our days, that we may apply our hearts unto wisdom.
The wisdom to which we are to apply our minds is the wisdom of God. This is found only in the Bible.
2 Timothy 3:16 All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: 17 That the man of God may be perfect, throughly furnished unto all good works.
I hope you have found this helpful.
God bless you,