Issues concerning the commitment of a minor?

So, I have a disturbed and bipolar character in one of my stories who, after a severe manic episode in which he nearly killed his parents, was committed to a psychiatric hospital at 15 years old. I've been researching everything I can as much as I can, only it's been difficult finding information about mental health laws in relation to minors, specifically about release. I've heard it's required for a minor to be released at 18 years old (well, not so much heard as *saw* on the Criminal Minds episode Lucky, where a criminally insane patient was released against the recommendation of his doctor, which is why I'm dubious. TV shows aren't known for being incredibly accurate, being allowed dramatic licence and all). I haven't decided on where he lived except that it was somewhere in the United States, so I realize it's a rather broad question. But is this true? And would they still release him if they genuinely believed he could be a danger (to others or himself)? I know specifics would change from state to state, but in general. Also, if there are any extra details (about anything) that I should be aware of, or links to helpful sites about mental health or mental health laws, I would be so grateful.