I have pre-finished hardwood floors on my entire first floor. House is about 8 years old and most the floor looks great except under a table. There are spots under the table where the finish appears completely worn off and the wood is now dull. I'm concerned if there was a spill something will soak into these spots. Is there something I can do to protect these spots till I'm ready to have floors refinished? Don't want to do that now as I still have young kids and most the floor looks good. Not sure if I can track down manufacturer of flooring as the place it was bought went out of business. My builder might remember that brand. I was hoping to use something like minwax reviver, but they don't recommend it for pre-finished.

There may still be finish that has soaked into the grain that can protect the wood.
Using "felt" floor protectors under chairs will prevent scratches as long as they are clean. Soiled protectors will attract grit that will act like sand paper to wear the finish each time the chair is slid across the floor. You could also glue leather cut to the pattern of the chair leg and glued on with carpenters glue
Peel and stick protectors are easy to change.
The trick to installing them in the first place is to use some sand paper or a scrubber to clean any dirt off. Then take some duct tape pressing the sticky side to remove any dust until the tape sticks. A protector will adhere after this cleaning.
Periodically turn the chair upside down and scuff the protector with a dull knife to take off any glaze/dirt.
I also recommend putting an area rug down to cover worn areas until the whole room needs a coat of finish, then I advise two coats, as long as the first coat has no adhesion problem.