Unable to load into worlds made before the update and is not a Realm

I have logged into minecraft 2 days in a row. I am able to load into my Realm and a world created just yesterday, but anything else I am not able to load. It pans over to a loading screen, but just as fast as it happened, it stopped, and would not allow me to load the world. I have multiple worlds made before the update, but none of them will open. I have restarted minecraft, updated the launcher, and even restarted my computer, but even after everything I have done, I am still unable to load my worlds.