There is no doubt that the Bible is one of the most valuable historical documents that we have. Textual critics date most of the OT to around the time of the great Athenians -- Plato, Aristotle, Thucydides, Herodotus, Xenophon etc. But it also seems clear that the assembly of the OT did include at times much older documents. Just which those are is of course something that textual scholars continue to debate.
For my money I see Exodus and probably Genesis as very early. And I base that on the view of the Gods found there. The Greek Gods were generally very powerful and effective figures. Nobody pushed them around. But YHWH as described in Exodus is rather pathetic, much more like the only barely effective Gods of earlier times. He has the Devil of a time (if I may use that expression) in getting the Pharaoh to do anything and it is only after YHWH has visited plague after plague on Egypt that the Pharaoh relents a little
But that is only the start of YHWH's troubles. Now he has to keep the Israelites in line. And he frequently fails. They go off after other Gods all the time. So I see Exodus as a true account of a quite primitive people -- much earlier than the sophisticated Greeks.
And that is valuable. We have no comprehensive account of such a primitive people from any other source. We have a few scraps of cunieform but that is it. So how accurate is the OT as history? From what I see, it always has the last laugh. Things in it that were once dismissed as myth keep being confirmed as real by archaeological discoveries.
So what are we to make of the days of Methuselah, when some men lived to be nearly 1,000 years old? As is usually alleged, it could simply be a mistranslation. In earliest times there were a variety of number systems in use and interpreting numbers given in one system as if they were from another system could give absurd answers. They could be out by a factor of 10, for instance. That this was the mistake is now well-argued for, so instead of Methuselah living to 969 years, his age is now given by some scholars as 96.9 years -- which is very plausible.
I am reluctant however to say that anything as recorded in the Bible is wrong or mistaken. People who claim that often have to eat their words. So I have an explanation which makes sense of the literal Bible account.
Most people these days accept it as entirely likely that there is intelligent life elsewhere in the universe. But they also see it as quite unlikely that we will ever get vistors from extra-terrestrials. Why? Because the distance between alternative biospheres is so great. You would need to travel several lifetimes just to get from one biosphere to another.
But what is a lifetime? I don't think it stretches credibility too far to say that there may be some beings somewhere for whom 1,000 years is a lifetime. And for such a people, interstellar travel may be a more attractive and plausible idea.
So Genesis chapter 5 could be seen as showing that there is such an extraterrestrial people and that they did once visit us. And that they were humanoid is not a stretch too far. As biologists say, form follows function.