There is really nothing in the Bible about them using moon cycles to count their ages. There are many theories of why humans lived so long.
Out of all the things Genesis claims, the existence of Giants isn't that far-fetched. There have been elephant men, dwarfs, red, yellow, blue. It doesn't seem crazy to me that there would have been people who appeared to be giant. recipe for supreme intellect.
I can see that. In fact, it says somewhere in the Bible that in the end times, things will be as they were in the day of Noah. According to Enoch in his three books as well as the Book of the Giants, it appears as though these fallen angels/ and or Giants did do genetic type experiements/alterations to to Dna, or the seed of life as it is/could be referred to. According to things I've read also, that is the one thing that God does not like. Humans playing God and messing with the genetic code as he can look past all sin but that. Seems ironic then that humans have recently began the cloning proccess and genetically modifying seeds. I have read most of the first book of Enoch and it paints a pretty clear picture of why the flood was sent. For all the naysayers on the Bible, every ancient culture and religion has a flood type story so there is a lot more information out there on the matter than the Bible. Enoch of course was a part of the Dead Sea Scrolls and for some reason was known to Constantine but he decided not to put it in our version of 'The Bible' at the council of Nicea. However, I don't think that fallen angels literally mated with women. I think they merely corrupted the off spring from Adam's son Cain and his lineage from an early age by teaching them 'forbidden things', although, who really knows? I agree with modifying the genetic code though and getting things like Sierens and perhaps even the dinosaurs were genetically altered reptiles and could be the reason they don't exist today... Random and crazy thoughts to some, but I assure you these ideas come from a lot of reading of ancient texts and a good amount of the History Channel Love that channel.