Current year
1603
Named by
The Authority
Archives / World Lore
The Golden Age
The present era, so named by decree rather than by agreement
The current era of the Familiar Lands, running to the year 1603.
It is called the Golden Age as per Authority's decree — which is to say that the name is official rather than descriptive, and that somebody decided it should be called that. Whether the lands themselves have noticed is a separate question.