Unfortunately, there's no way to time-date the item with significant accuracy. Though it's obviously a tag of some kind, there are many kinds of tags, of course. I assume there's nothing marked on its other side, because you didn't mention or show the other side. Military tags tend to have some kind of unit designation on them, such as 15th Infantry or 12th VA (regiment). Based on its apparent size in the photo (you gave no measurement), I think it is most likely to be a hotel room key tag. It could be a cow-tag or other animal tag, but those are generally larger, so they can be easiiy read from a distance.
Regards,
Pete [P.C. George]