I’ll take a chance and see if anyone can make a better guess than I can. :-)
I would guess the key was produced in the very late 1700’s or some time in the 1800’s. Because it has a shoulder near the operating end of the key I will suggest that it was a key for a cabinet, chest or possibly a closet. A key with no stop would allow inserting the key through a door from one side without obstruction.
The top part as shown in the picture is called the post and in your csae a drilled post. These keys are sometimes called drilled keys, or pipe keys and sometimes called barrel keys, depending on where you live. The round part below that and the projection from it are called the bit and the places that have been cut away in the bit are called ward cuts. They exist to allow the key to bypass obstructions inside the lock so that the key may be turned to make contact with and throw the bolt of the lock. The reason the round part of the bit is hollow indicates that there may have been an obstruction to prevent insertion of a key without it and that obstruction would have moved with the key when it was turned.
It is a very nice key and looks to be in very good condition. From the general appearance I would also guess it is made of malleable iron. Hope that helps.
BBE.