Nice keris picit. These are talismanic keris. As suggested the imprints are supposed to be done with the fingers of the maker. They are certainly less common, but not paticularly strange.
I don't think the seller's info is that far off. Pictures never tell the whole story, but this could very well be 16th or 17th century as far as i can tell. Is there a sheath? Can we see the pesi (tang)? What is the blade length?