I completely agree, maddyone that if anyone hurt my loved ones I would want them to suffer. Badly.
But that is the reason we have the rule of law, not vengeance.
The law is supposed to be impartial and objective, and the law says that under 18s are, in these circumstances, minors, with the protections that that entails. The fact that this boy is 'nearly 18' is irrelevant.
If we start messing about with the law, it may as well not exist, and we would have anarchy.
Sentencing is another matter, and in most cases gives judges discretion to take account - within the law - of special circumstances. In this case, it is likely that the boy's previous convictions will be taken not account, and he will be detained at Her Majesty's Pleasure - in other words, until it is very clear that he is no longer a danger. That may mean that he spends decades in jail, and if that is necessary, so be it. If he can be rehabilitated and learns the error of his ways, he may get out sooner.
It is not, however, for popular opinion to decide. That way madness lies.