Paul's assertion is exactly correct. No one has ever been righteous in God's eyes who was also a nonbeliever. All of us have spent all of the earliest years of our lives as unbelievers. All who become saved believers spend all of the latter years of their lives as saved believers. Paul is talking about the former "all". Paul knew as well as we do who were called righteous in the OT, so he couldn't have meant all people for all time in God's eyes. Paul did not contradict himself, or any other scripture.
Everyone believed in those days. I don't think there was a single account of an atheist. The righteous of the OT were chosen by God to do specific tasks, just as our Lord Jesus Christ chose His apostles, including +Paul.
According to +Paul, no one can be righteous because all have sinned (through Adam). We are made righteous by baptism, yet as far as I know the OT righteous were not baptized. In fact, Christ specifically went to pull the rigtheous out of hell -- but one can ask if they were rigtheous, why were they in hell to begin with? And why were Adam and Eve among the righteous?
Yet, clearly, Job is not portrayed as someone who was anything but perfect in God's eyes.