As far as the exact region i could not say, but it is probably safe to say Jawa is the place of origin. I am curious to see if the pesi has a hole, or the remains of a hole, in the end of it. The size seems right for talismanic purposes and often these keris were hung by these holes in special places of importance. It is possible that this keris was never intended to have a hilt at all and it would be no surprise then that it would also be sheathless.
Given the look of the material in the photo at least i would also not be surprised to find that this blade is at least 1700s if not older.
