Serona was a Romulan Rite of Transition and was a rite of warriorship.

This rite was typically taken at the age of 30 by adults who pledge their service to the Romulan Star Empire. It was a formal requirement by all citizens and to ignore the rite was considered an act of treason. Serona can be both a public or private one though those Romulans who are proud and traiditional tend to prefer a public ritual, which tend to emphasize personal feats of strength and endurance that demonstrate the citizen is worthy of being considered a descendent of a Romulan hero.

Once the rite is taken, military service begins which is a five year requirement; after which retirement is an option that most Romulans take while others remain in their field either out of a greater sense of duty or for adventure or possibly as a way of advancing their career.

(Last Unicorn RPG: The Way of D'era: The Romulan Star Empire)