It’s largely mythical, based on a very reasonable sounding idea — that copper replaced stone because it was better (and it probably ain’t for a lot of common uses of in prehistoric antiquity), that bronze was better than copper, that iron was found to be better than bronze, just so just so just so.
IMHO it’s goofy to use these as a date for anything, because it isn’t a real date at all. Some cultures were still using stone tools (the Americas were chock full of that) and didn’t develop bronze until at least a thousand years after its tool use declined in the “Old World”.
In any case, it’s better to use actual dates and date estimates based on the radiometric tools developed in the last 70-80 years. Back when these ‘ages’ were posited, there was stratigraphy and not much of anything else. Even dendrochronology antedates radiometic dating, but clearly using radiocarbon dating on individual tree rings helps calibrate the dates.
-suggests that what had once been labeled an early iron-smelting site was actually a copper workshop that utilized iron oxides as a flux-
First flux capacitor. Maybe where Doc got the idea. ;-)