During what century, year, or time period does The Alchemist by Paulo Coelho take place?

the 1700s is very possible; however, alchemy was practiced the most during the Middle Ages and was labeled as the medieval ancestor of chemistry. Therefore, it is also likely to have occurred during the Middles Ages (roughly the 4th or 5th to the 14th or 15th centuries). There is some reference to it during the Renaissance, as well, which would be 15 to 17th centuries)

In rereading the given sections of the novel, no where in Prologue is Oscar Wilde referenced, and the story can cannot be labeled strictly to him, as it is a famous myth that I have heard and read in many locations. Furthermore, there is no mention of a plastic curtain, but, instead, "a curtain of colored beads." Beads can be made from wood, stones and various other materials other than plastic. The mention of a plastic curtain has been posted various places on the web, so maybe I just missed something, but I saw no reference in the book. 

Again, though, as the time is not written anywhere in the book, it is hard to label it with anything.