How old is GOLD?

In my grandmother's jewelry, we have found a ring that is simply stamped with the word GOLD, no specific karat marking.

I think this ring actually belonged to my great or even great-great grandmother, so I would not be surprised if it is from the 1800's. I am simply trying to get a gauge on how far back in the family it goes. It is a small band, appears to be rose gold, originally set with 3 small (2-3 mm) round opals in prong setting.

have just never seen anything stamped with just 'gold' Could get photo if that helps