Final answer:
The argument that Saturn's rings might be old is based on the idea that they resulted from the break-up of a moon early in solar system history, a more chaotic time when such catastrophic events were more likely. Additionally, it is argued that the rings could be composed of primordial debris that never formed a moon, also indicating an ancient origin.
Step-by-step explanation:
The argument suggesting that the rings of Saturn might be old is based on the hypothesis that these rings could have been the result of a catastrophic event that occurred early in the solar system's history. One theory posits that the rings were formed through the break-up of a moon the size of Saturn's inner moon Mimas, struck by interplanetary projectiles that were common during the early chaotic stages of the solar system. The plausibility of such an event decreases for more recent times, as the solar system has since become a more stable environment, making a recent break-up less likely.
Another hypothesis contrasts the break-up scenario by proposing that the rings of Saturn consist of material that never coalesced to form a moon in the first place. This would underscore an ancient origin since the early solar system was rife with smaller particles and debris that could accumulate into rings but not large moons due to mutual gravitation and collisional forces in Saturn's vicinity.
Consequently, these arguments lean towards the rings being an ancient feature of the solar system, persisting over billions of years since their formation.