Nice key! What is its length? Presuming it’s a large key, I would think it went to a door. My guess is that its probably 18th century. It has a fancier bow (handle) than most, and the ward cuts on the bit (the flag-like projection) are very intricate. Wards are obstructions that prevent a key from turning unless a corresponding cut is made on the key. (if you are already familiar with key terminology, forgive me for defining everything.)
