All civs get a single golden age lasating 20 turns, there are 2 triggers for this and a civ gets its golden age when the first one occurs:
1. The civ's special unit kills a non-barbarian unit.
or
2. The civ builds a wonder, the game then does a check of all the wonders that civ has(both captured and built). Each civ has two special traits (for example, the Egyptians are Religious and Industrious), call them trait A and trait B. If the civ has at least one wonder corresponding to trait A and one corresponding to trait B, it gets a golden age.