Plenty of memorable fun moments in this Monty Python classic.  I shared it with my 13 year old and I don't have any reservations about a teen or late preteen watching this movie.  A mildly suggestive scene in the castle that houses only women is tame by 2013 standards.  Some violence with blood that is absurd enough to be comedic and acceptable to most 12 to 16 year olds.  This is a delightfully stupid movie and it helps if someone in the room has seen Monty Python before so that you can help explain to newcomers the disjointed, time warping, Python style of story telling.  The "monster" in the cave scene is a classic that was just as funny now as it was decades ago.  If possible watch "And Now for Something Completely Different" by Monty Python first and then watch this second.