Asteroid family is as old as the Solar System itself
 

To date, astronomers haven't seen asteroid families (that is, asteroids with a common source) in the Solar System older than about 3 billion years -- well after the star system came to be 4.5 billion years ago. However, they'll have to rethink their...

https://www.engadget.com/2017/08/06/...teroid-family/