“黄金时代”一语出自何处？

黄金时代(Golden Age)这一词来源于古希腊Hesiod诗人的《工作与时日》(Works and Days)，大约在公元前700年。
对于定义性的东西，几乎都可以在维基百科找到答案。以题主的黄金时代为例，摘抄维基百科Golden Age部分内容如下：The term Golden Age (Greek: Χρυσὸν Γένος Chryson Genos) comes from Greek mythology and legend and refers to the first in a sequence of four or five (or more) Ages of Man, in which the Golden Age is first, followed in sequence, by the Silver,Bronze, Heroic, and then the present (Iron), which is a period of decline, sometimes followed by the leaden age. By definition, one is never in the Golden Age.
By extension "Golden Age" denotes a period of rimordialpeace, harmony, stability, and prosperity.希腊神话将人类生活在地球上划分为不同时代：黄金时代、白银时代、青铜时代、英雄时代、黑铁时代(当下)、灰铅时代(有时候会有)。黄金时代的引申义为和平、和谐、稳定、繁荣的一段时期。

接着追溯，维基百科词条Ages of Man，你将会看到：

The first extant account of the successive ages of humanity comes from the Greek poet Hesiod's Works and Days (lines 109–201). His list is:
Golden Age – The Golden Age is the only age