Uh, am I allowed to use Steven Saylor as a source here or he is too much of a writer? AFAIK his books are decently researched.

If yes, the big deal was 16 the first time being allowed to wear a toga. And wear the iron ring of citizens. Or gold, if he was patrician. First, get off the bulla, the protective amulet worn at boyhood and sacrifice it to the household gods. Get bathed, get shaved the first time because it was forbidden before. Put on the toga with the help of slaves (damn thing was difficult to put on right) which too was forbidden before, go to church (pagan) and get a divination done, have a walk on the Forum and talk to adults and show off the toga, get enrolled in the citizen census, and have a party at home. Soon, military service would begin. According to Wiki, it was held on the festive day of the god of freedom, Liber, the day being called Liberalia, but according to Saylor, it would be the 16th birthday. Source: Steven Saylor: Rome, Empire etc.