Aside from mentioning that he partied pretty hard in the past, there's really no sex, drugs, or violence in Ecclesiastes. He does say that there's a "time to kill," but we don't actually see any throats getting slit. It's more of a think-piece than a full on blockbuster—more My Dinner with Andre, less Terminator 2: JudgmentDay (that would need to be Revelation, of course). Yet, if someone made it into a movie, we could see it getting a PG rating—just to make the movie seem more serious, and to make sure you know it's aimed at adults (since it definitely is). It certainly has "adult themes," just not the sexy kind.