As we go further into Genesis, a lot of this stuff is foggier to me, so please bear with me.
There are a few significant things I know about their ages. First, their extremely long lives resembles the Sumerian King List, except not to quite that degree.
http://en.wikipedia.org/wiki/Sumerian_king_list
Some of these Sumerian kings supposedly lived tens of thousands of years. From the Wikipedia article, after the first 8 kings there was a flood, and then a new series of kings who only lived for hundreds of years instead of tens of thousands. There are a couple versions of Sumerian and Babylonian flood stories, which strongly resemble the one of Noah and the ark. See this website for an example:
http://www.religioustolerance.org/noah_com.htm
I'm certain that there was more than one flood story by the Sumerians and Babylonians, because I remember the names of two different heroes.
Okay, getting back on track. Another important thing about their ages is that they were used by the Jews in the Middle Ages to calculate the supposed beginning of the world, which they base the years of their calendar on. More specifically though, the ages at which they had children.
According to my book, it says they thought the date of creation was October 7, 3761 B.C.
The significance of the different sons of Adam are sometimes explained as representing the development of culture and technology. For example, Cain (Kayin) is a smith, and Tubal-Cain means a smith of Tubal. I believe the scriptures explain some of that stuff. I've heard that Seth's bloodline is actually a copy of Cain's, with some minor differences. So it would be one of several duplicates in the Bible.
The story of Cain and Abel itself is explained as a dispute between the farmers and the nomads (there is a corresponding Sumerian myth for this as well).
http://www.sacred-texts.com/ane/sum/sum09.htm (see "Inanna prefers the farmer")
Okay, going to Enoch. He's a very interesting character, but a lot of the interesting material isn't in the Bible itself. There's a few things: for example, the Ethiopian book of Enoch. You can read a translation of it online on various sites.
http://exodus2006.com/ENOCH.HTM
This was written sometime after the last officially recognized book of the Old Testament, and before the New Testament. Apparently it was very influential on early Christian thought, and is even mentioned in the book of Jude.
It also expands on the story of the "sons of the gods" that you read about. They are usually thought of as angels, or sometimes fallen angels.
Here's what my book says about Enoch:
The fact that Enoch is described as living 365 years, whereas his father Jared lived 962 years and his son Methuselah lived 969 years, seems odd. Is it a coincidence that there are 365 days in a year; that is, in the complete circuit of the sun across the skies? Is it possible that the verses given over to Enoch are all that remains of some Babylonian sun myth?
What is meant by saying that Enoch walked with God and was not is uncertain, but later traditions made it clear that the usual interpretation was that he was taken up alive into heaven as a reward for unusual piety.
It was supposed by the Jews of post-Exilic times that in heaven, Enoch was able to see the past and future of mankind. Between 200 B.C. and 50 B.C., several books were written purporting to have come from the pen of Enoch, describing this past and future. They are purely legendary and are a form of "religious fiction" which was fairly common in the post-Exilic period. (Some of it, as we shall see, found its way into the Bible.)
Jumping back to the sons of the gods, according to Reading the Old Testament (a site I linked to earlier) they were members of the "divine council." Apparently they thought of heaven like a king's court. I didn't really understand it too well, though.
http://www.thebricktestament.com/gen...n06_01-02.html
This looks good enough for me. It really is a rather cryptic passage. I don't know if they know of a possible origin for why this verse is there, like how some of the other weird stuff came from the Sumerians or Babylonians.
*is tired*