VERY interesting find--- legend and general design indicates it's supposed to be a copy of an Elizabeth I coin, but the bust looks more like Charles I! It appears to be lead (very common for tokens in old England to be made of lead). I also agree it appears to have some major age to it.... and also very hard to tell if it was struck to serve as a counterfeit coin or as some kind of (maybe) British medal, token, jeton, etc.? As to what century it was struck-- looks like it could have been struck as far back as the 1600s, maybe as recent as the 1800s. And what the heck was it doing at a US civil war site?? I do have a base metal "6 pence" of Elizabeth I, but it appears to be a hammered piece, not nicely round like this piece.