Well, it’s a motif that you find in a lot of mythologies and belief systems. In scripture you have the first age, of Adam, when God walked and talked with humans and people had enormous lifespans. In Sumerian mythologies you have the early kings who lived for thousands of years. In Egyptian mythology, the gods first ruled Egypt and the Greeks divided history into respective ages, commencing with the Golden Age when Kronos ruled the world and humans lived among the gods. The Greeks (Hesiod) and Romans (Ovid) had this idea of an Age of Iron, when people became greedy, warlike and impious. Although they may have been influenced by Greek, Roman and Christian thought, the Irish cycles of invasions also echo this cyclical and sequential division of time with civilisations or cultures rising and falling. I believe that numerous other mythologies around the world, including Aztec, Mayan, Indian dharmic and Buddhist traditions also have ideas of different ages and cycles of time. Indeed, Tolkien also used these motifs in his fantasy cosmology of Middle Earth. Interestingly enough, the Etruscans, who often get forgotten about in terms of the Classical Mediterranean civilisations, divided their history into ages or periods and, seemingly, even predicted their actual historical demise. As an aside, I’ve often wondered if there were not some cross-pollination of Etruscan and Celtic traditions as there are some tempting parallels between druids, Celtic religion and culture and that of the Etruscans, who neighboured the Celtic peoples, however, it would only ever be conjecture because we don’t know enough about the Etruscans.
Other ideas that are connected to these notions might be those of a great flood or disaster – flood myths are found the world over – and it is not too farfetched in my opinion to consider the possibility that there were some vague, ancient folk memories of real disasters that were then transmitted orally over millennia.
One theory about the Minoan civilisation is that it was brought to its knees after the eruption of Thera: the subsequent tsunami, volcanic cloud of ash, famine and destruction destabilised the civilisation completely – there is even evidence of cannibalism. Archaeologists have also found Minoan statues of gods and goddesses, including the famous Snake Goddess, that were deliberately smashed, their temples burnt down and desecrated, and it has been speculated that the people may have turned their anger on the gods who no longer protected them or that there were some kind of religious civil war. I reckon that the Atlantis myth may be connected to these events. In the mythology of the Brythonic peoples, legends of a city that sank under the sea because of its wickedness are also found in respective Cornish, Welsh and Breton traditions – probably the most well-known being that of Lyonesse.
So, there are a lot of commonalities between among numerous traditions and the Old Testament also contains allusions to these too.
If you’re interested in a psychological take on this, I’d recommend Julian Jaynes, The Origin of Consciousness in the Breakdown of the Bicameral Mind (1976) in which he argues that ancient people may have thought “bicamerally”, in a different way to modern humans, and this breakdown is reflected in mythology and writing. Jaynes is not without his critics, but the book is fascinating in itself even if you don’t agree with Jayne’s premise.