Honestly, it really depends on maturity.
I think that parents underestimate kids' maturity. I think kids should be able to read books like this, if they think they can handle it. It wasn't over-the-top violent, but it still was. At the beginning of the book, several teenagers must cut their hand, so they can drop their blood in a bowl to choose their faction, where they will live the rest of their lives (if they survive initiation). One initiate is stabbed in the eye with a butter knife by another initiate, and several are beat up. There is one case of suicide. There have been several attempted murders, thousands of deaths that aren't seen, and only few that were. Around the end of the book, most of the Dauntless are controlled by a simulation that forces them to kill the Abnegation. Tris must kill several simulation-controlled guards to stop the simulation.
In order to get past initiation, the initiates must go through their fear landscape, a simulation that has the person go through their worst fears. One of the main protagonist's fears is intimacy, and is later mentioned while talking to other initiates. "I'm afraid of.. intimacy." "Intimacy? You mean like... sex?"
There is barely any cursing, only mild uses of damn and hell. But they aren't so bad, in fact I hear them at school all of the time. Though, some parents might not like their child seeing these words. But, I think that if they know not to say them, it's okay.
Overall, it's a really great book, 10/10 would read again.