It goes back a little earlier, but if you pardon the pun, Young Earth Creationism is itself a fairly young theology. The predominant idea behind YEC stems from

It goes back a little earlier, but if you pardon the pun, Young Earth Creationism is itself a fairly young theology. The predominant idea behind YEC stems from the 1920s and Seventh Day Adventism, particularly Ellen G. White who claims she had a vision of man and dinosaurs walking the Earth together. Her claims would have disappeared into history as the ramblings of a cultish leader until they were more or less popularized by Henry Morris and John Whitcomb—and yes, in the 1960s. There's a lot of bonkers theology that rose to popular culture during that time period. Incidentally, it's also when Gog/Magog were ascribed to Russia (because of the Cold War), and if you read the papers by Dr. Paul Tanner on the subject, it becomes quite clear that the extent of exegesis performed basically amounts to cross-linguistic homophones—that is, that one of the regions (princes?) listed in Ezekiel, Rosh, happens to sound like the Indo-european root "Rus." Therefore, obviously, it's Russia... Facepalm. I'm a Christian, and I lean more toward Dr. John Walton's view of Genesis 1, that it was intended as a functional description of the created order. We forget that the culture that produced the Bible was vastly different from our own, and the Israelites saw things as "uncreated" if they served no purpose. That is, the idea of nihility (or creation ex nihilo) are modern ideas that we have imposed on the text in order to satisfy a narrow reading of scripture. Even if you're not a believer, as one of my sibling comments suggests, the oral tradition itself seems to capture events from the end of the last period of glaciation. But to assume people lived for 100s of years despite the fact we know almost nothing about the period during which the primordial history (Genesis 1-11) was authored (and we know little about how/when it was redacted, though most probably during the Exile) is naive. The ages most likely conveyed some meaning themselves, because the early Israelites were much less interested in exacting chronology than we are. Here's an example: Sarah is said to have lived 127 years. Interestingly, 7 being the number of completeness/perfection in Israelite culture and 120 (or 110) representing the same in early Egyptian culture seems to convey the idea that she lived the "perfect" (or "complete") life as both an Egyptian and Israelite woman. This may be stretching the numerology somewhat, but if you step outside YEC material, there is some scholarship that makes a pretty strong case for this reading.