@anderstallvik It kind of works when they are marginalised / semi-mythical groups that don't integrate much with the short-lived mainstream. That's the default in the German The Dark Eye game. Of course it means the world is terribly anthropocentric and the other ancestries are PC fantasies 90% of the time - so not the greatest solution.
if you have only one ancestry with long lifespans, you might go the cultural route and have them mostly shut up and roll their eyes when the younger folk talk about how unprecedented sth. is.
Also worlds should be big. The fact that one thing happened three hundred years ago two continents over might not be known to even a handful of folks from million strong ancestry that doesn't live there.