As well as it being a long time for a 16 year old, it also means he's spending all the formative years of his life behind bars in a way that doesn't apply to a 30, 40 year old sentenced to 27 years. All the years when everybody is laying foundations to their life, choosing a career, finding a partner, building a home, he will waste in prison. Even if he did get out after 27 years, he would have nothing to come out to and would be completely institutionalised. That's one of the reasons why I think he'll never be passed for release by any parole board.
Fear of institutionalising juveniles is one of the reasons why they are usually not sentenced to as long as 27 years even when they kill. By passing down such a sentence the judge as good as said that AC will never be fit to live an independent life.