The Age of Discovery was a time period that occured in Romulan society.
On reference stardate -3/8704.2, Vaonus of Calanista postulated that Romulus sister planet of Remus was inhabitable which heralded the start of the Age of Discovery. Originally, legends stated that life existed on other worlds but this was the first time scientific data supported this theory. (FASA RPG - The Romulans module: The Romulan Way: Game Operations Manual)
- The FASA RPG material predates canon elements that showed Remus was a harsh uninhabitable world, however, its possible that the Age of Discovery was more about the rediscovery of space flight technology then simply colonization of Remus.