It has been there for a while... Depending on the makeup of the shoreline...
If it is heavy black sand in areas, has runoff from areas, even salinity matters. Personally I would gamble it been buried longer. Look at a post I made a few weeks back with a silver spoon ring. That has been "under" for quite a few years... Not all areas have the "cookie coin" effect on built up corrosion around the silver...
Don't post where you are hunting on the board... Keep location to yourself, but areas do matter even with corrosion... The other items dug from that area, even coins, how new? Even a coin from the 80's is now 30 years old... Something to consider....