First question: is it made of iron or brass? I can’t be sure from the picture.
If brass, it’s a modern gift shop/interior designer’s item.
Otherwise, it’s probably British early-mid 19C. While it looks like a key for a warded rimlock, those usually had a bridge ward. Locks with sash wards but no bridge ward are almost always mortice locks. The bullet wards are more common in European locks, but also sometimes found in good quality early 19C locks. What puzles me is the size - it’s too big for a mortice lock.
It just doesn’t look quite right, but it could be a genuine high quality key. But back then, unlikely to have a number stamped on it. On balance, I am suspicious.
