“Is the book of Job the oldest book in the Bible?”
That’s a great question and one that I can’t really answer for sure. People have come to various conclusions in answering that question. Despite the variations, most scholars agree that Job was a man from the time of the Patriarchs, but before Moses was on the scene.
Before we get to answering the question, here’s a great video overview of Job if you’re not overly familiar with the book itself.
In R. Reed Lessing and Andrew E. Steinmann’s book Prepare the Way of the Lord where they discuss the history and Christocentric themes of the Old Testament they suggest that “though is is no clear who wrote the book of Job [though they tend to Agree that Job did and discuss that in the paragraph leading up to this comment], the book’s era must be sometime during Israel’s time in Egypt.” (p. 280)
They go on to lay out the genealogies of the men with whom Job interacts in order to show how they are related to other individuals mentioned in Scripture. At the end of the section they say this, “Since Eliphaz is at least three generations from Esau, it stands to reason that Job is about the same – at least three generations from Esau and Jacob, or during the Egyptian sojourn. Bildad’s genealogy suggests the same.” (p. 280)
Jacob and Esau were born in 2006 BC and the Exodus from Egypt took place in 1446 BC, so Job appears to have taken place somewhere in that window. (Timeline in The Lutheran Study Bible for the introduction for the book of Job)
Based on the things Job does and responsibilities that he has in his home and things that are not mentioned (tabernacle, temple, and so on) it also seems to suggest that he is living prior to the Levitical priesthood and the Torah. (p. 280)
Since the Torah (Genesis-Deuteronomy) was written by Moses, it does seem to suggest that Job came before that, but we don’t have definite timelines for it from the book of other historical records. We can only make assumptions based on what the text provides.
Hopefully, that helps.
Be sure to let me know if you have any questions.
Blessings on your day!