'It is surprising if it is true that it only dates back to 18th century; as a folklore symbol it goes much further than that.'

Jim,
Nobody suggested that. I simply said that most of the ballads quoted that use the motif can't be traced back any further, but some of them can be traced back to the 17thc. I can't say that I've seen any of the quoted ballads that can be traced back further than this though, not in English anyway.