Cassini’s data indicate that most of Saturn’s rings are probably as old as the solar system itself — about 4.5 billion years. Earlier observations, during the Voyager flybys of 1980 and 1981, suggested the rings might be as young as 100 million years, the result of a nasty breakup between a large comet and an icy moon. But Cassini observations show that the rings could not have been produced by a single event.
https://www.space.com/37669-saturn-rings-mysteries-nasa-cassini-mission.html