It's hard to tell the age of an African piece. The one I showed from the book is documented. The author states that it came from the collection of the Fathers Capuchins from Antwerp (Belgium) with as collection date : between 1880-1920.
I doubt that your piece is as old, but it probably dates from the 50's or 60's. In the beginning of the sixties Congo became independent and a lot of colonists returned to their homecountry, bringing with them these jewels.
I wouldn't ask the seller for more info as he gives the wrong continent as place of origin.