I'll give it a shot.................. It's hard to date rings in my opinion cause not much really changed over time.If I had to make a guess I'd say it's at least 17th century (could be earlier).And is a signet ring.Here is one that was dug here in the states at jamestown that is very close to the way yours looks to me as far as the thickness of the band & general shape.
Take Care,
Pete,