In the original trilogy they could be vague about time periods. They could be vague about how long ago the Old Republic was, how long ago was the heyday of the Jedi and how quickly or gradually it ended. It was only a couple of lines of dialogue. We were supposed interpret everything in terms of metaphors anyway, and the source material – Hidden Fortress and samurai TV shows in Japan and World War II movies and all that – was not offering a consistent sense of how long ago the “good old days” were.
The obvious solution is just don’t do prequels. Let the mysteries of the past be mysterious. The Star Wars prequels were shit, J. J. Abrams’ Star Trek reboot was pointless, the Alien prequels stopped being any good exactly when the writers tried to stitch them together with canon properly.