(classical mythology) the first and best age of the world, a time of ideal happiness, prosperity, and innocence; by extension, any flourishing and outstanding period WordNet 3.0 & Open English WordNet

The term Golden Age comes from Greek mythology, particularly the Works and Days of Hesiod, and is part of the description of temporal decline of the state of peoples through five Ages, Gold being the first and the one during which the Golden Race of humanity lived. Wikipedia

Far-gone period of primordial peace, harmony, stability, and prosperity, from Greek mythology Wikidata

The oldest and best of the Classical Ages of Man, when people lived innocent lives of happiness and prosperity. Wiktionary