One of the most violent films I've ever seen...still it'd be OK for teens
As CSM points out, it all depends on your faith. If your child is very religious (especially Catholic) and is interested in seeing one of the most told stories performed in a very stylized, graphic manner, then I'd say to wait til they were in their later teens before presenting them this film. If you are non-religious like myself, and just wish to see the movie as a movie, and not as an affirmation of faith, maybe wait until you've seen more mature content so you can handle this. It is relentless in its portrayal of Jesus' torture; you will become very familiar with the sound of Jim Caviezel moaning. His performance has been praised, and he does do a fine job in the beginning, expressing the agony of Judas' betrayal. But all he does is wince, moan and scream for the entire film, get spit on, scourged and beaten. Gibson shows us these scenes with slow motion, and especially focuses in on Jesus...falling. We understand the significance: this is a holy man that several groups despised and hated, and crucified because they thought his claims were blasphemous. Don't hammer us over the head with it. The movie does have a lot of interesting symbolism, especially in the specific choice of how Satan looks, and how Judas reacts with life after he turns Jesus over. But a lot of that is taken away with the excessive nature of the violence, like "Unbroken" with Tarantino blood splatter.