[Something Paul has come to note is that many universes have more complete understandings of their histories and planets than his own does. He's not sure how much his answers end up satisfying people, but he's optimistic about these ones in particular.]

At least ten millennia. That's when the Guild of Navigators arose, and the sand worms were already on Arrakis when it entered into the historical record through them.

[Now it's his turn to be curious. He doesn't know all the planets of the empire - no one could, save the Guild, and even within that bureaucracy Paul would expect errors - but a recently new entrant should have been known to him.]

I doubt we hail from the same galaxy, but I'm always interested in hearing about others. What is your planet like?