This film is one of the greatest ever made, and definitely one of the most emotionally affecting. It's a very serious and tough depiction of the mind of a twisted, but not evil, nobody in the everyday world, and Robert de Niro gives one of the greatest performances ever onscreen. Travis Bickle, the protagonist, does monologue about many political, philosophical, and psychological things, and a lot of visual symbolism is expressed throughout, so that's why I think only a maturer audience would be able to understand and enjoy the film to it's fullest. The sexual content is only hinted at rather than fully exposed, and the violence isn't too horrible, so I'm pretty sure most would be able to handle it. Parents should also know that Travis is actually a 'psychopath' as CSM says, but instead an anti-hero, as he has too much passion & emotion, and too many morals, and the reason why he is praised for his violent actions is actually meant to be ironic. All in all, this is a film that could teach the crippled to walk and the blind to see, one that could change the lives of many, and one that every single person should definitely watch, no matter how dark it is.