I think if we accept the listed ages as accurate, that you give the best explanation.
The planet, the atmosphere, etc. changed over time. They lived in a different planet than we did.
http://www.chick.com/catalog/books/images/1254.jpg
You'll find yourself nodding you head quite a bit -- and here's the important thing; The entire book is based on SCIENCE.Chapter 14 - Effects of the Flood expounds on the subject extremely well, using plausible scientific theory and scenarios. It dovetails with Chapter 4 - The Age of the Earth (Why the Earth is not millions of years old) along with Chapter 6 (Inaccurate Dating Methods.)
Let's face it -- most of us at one time or another never altogether really bought those 600-900 year old ages, but never took into account the possibility of an entirely different planet with altogether different material "laws" that changed the entire pre-Flood "laws" of nature.