I think it is likely this boy, and that is closer to what he is, may well go on to display behaviour which will mean he will serve longer than the minimum. He has done a terrible thing, and it was premeditated but coming from a disordered thought process. He wanted her to die so he could have his life.... it's awful but he called the police, he didn't go on to kill others, he isn't a serial killer or a spree killer.
I believe life should mean life maybe within closed community living when age or infirmity make the likelihood of further offences really unlikely. Life isn't cheap while people have the ability to care about victims, while the press still reports these cases and life sentences are handed down.