What is the oldest known calendar? Where exactly was it developed? Who was responsible for its creation?
Let me introduce you Alexander Marshack, who in his book "The Roots of Civilization: the Cognitive Beginning of Man’s First Art, Symbol and Notation", published in 1972, proves that notches and lines carved on certain Upper Paleolithic bone plaques were in fact notation systems, specifically lunar calendars notating the passage of time. It was developed by Aurignacian culture, which was active in Europe and southern Asia between 47000 to 41000 years ago. This way it would make it the oldest known lunar calendar.
You may also want to search for an article by Judy Robinson titled "Not counting on Marshack: a reassessment of the work of Alexander Marshack on notation in the Upper Palaeolithic" published in Journal of Mediterranean Studies in 1992, in which she suggests that Marshack's discovery is just an over-interpretation.