The phrase "my spirit will not contend with humans forever" is notoriously difficult to translate. Modern scholarly consensus is coalescing on "My spirit will not remain in man forever," a statement affirming mortality.

As to the second part, the Sumerian folk talk "Enlil and Namzitarra" speaks of 120 years as an ideal human lifespan. Speculation about it suggest that this number is not meant to be literal, but comes from abstraction within the Sumerian mathematical system. The idea that the deity governs the length of a lifespan is also reflected in the Gilgamesh Epic, where the hero is trying to achieve immortality. Also, a wisdom text from the town of Emar cites 120 years as the most years given to humans by the gods. The idea that he will live 120 years is a way of saying his life will be the ideal length and no more, because he is mortal.

In the Egyptian Book of the Dead, the god Thoth reports to the creator god Atum: "You shall not witness wrongdoing, you shall not suffer it! Shorten their years, cut short their months, because they have done hidden damage to all that you have made." We see the same thing here: There has been offense to the gods, and life is cut off rather than continuing eternally.

So the teaching of the text, and the point of it, is a statement about mortality. Proverbially speaking, wickedness shortens life. "His days will be 120 years" means the ideal human lifespan will become shorter than it had been.

I can still believe the Old Testament is the infallible word of God AND make sense out of the text.

"Then the LORD said, "My Spirit will not contend with humans forever, for they are mortal; their days will be a hundred and twenty years."

1 - It appears that we are on the cusp of humans living longer than 125 years and have already had a few people come close to that number. Hypothetically speaking if someone ends up living longer than 125 years how would you interpret this verse in light of that event?

2 - How do you interpret the aspect of this verse about God not wanting to put up with humans for more than 125 years given that the Bible teaches that our souls are immortal? Isn't God going to have to put up with us for forever in Heaven?

I'm really curious about #1 and how you will reconcile that happening. My first, best guest would be that those who take the Bible as the infallible word of God will assume or come to believe that the person who has lived over 125 years is lying about their age or confused about it and that the documents verifying the age of birth are in error.

But should living past 125 years become commonplace that will become harder and harder to do and the problem with this verse is that there is not much you can do as far as interpreting it in a different way as far as I can see, not without some serious mental gymnastics. The big issue here being that if the Bible's statement that God will not let us live longer than 125 years is invalidated it is no longer possible to believe the Bible is the infallible word of God - which is the entire backbone of the Christian fundamentalist movement.