The main themes movies are rated with are: violence, sex, drugs, profanity, nudity, gambling or other types of mature content. However these themes are becoming more prevelant in movies these days and children learn about these things at a younger age so they should be confortable with these topics. These age rating stop the kids from coming to terms with these topics and it would be much better if they learnt about these things in a movie then through peer pressure and experience. Besides parents underestimate how much their children really know about these mature topics and the amount of swearing in a mature movie is about the same thing that you would hear in a high school. This is why I believe age ratings are pointless and should be eradicated as they aren't really protected the children from anything just making them want to watch it more, as something becomes more desirable when its not allowed.
The same applies to video games but its a slightly different scenario as it costs only 10 pounds to watch a movie but about 40 pounds to buy a video game.