Ages are a feature added in the upcoming Civilization VI: Rise and Fall expansion pack. Here's the lead designer Anton Strenger on the subject: Golden and Dark Ages are among the new events that can shift the course of your game’s history. They are significant, but temporary, changes to a civilization that last for an Era. They will open up new opportunities for players to change their strategies, and change the state of the game between the player and their rivals. Having a Golden Age affords huge bonuses to Loyalty and other game systems, but makes earning future Golden Ages slightly more difficult.