You can believe it or not, in theory wheel bearings are good for life !
But that only works if they always had grease, and never had water, moisture, or dirt in them.
If you jack up each wheel, spin it, and it is quiet,...or not much more than a whirrring sound, you can be 99% sure the bearings are good, no matter how old they are. Any bearing w/ a pitted or rough surface, will make a very noticeable growling sound.that grease won't stop. If I fine a questionable growl, I give it a shot of grease, if it doesn't quiet it, I'll change it. Otherwise they are good to go.