Earlier quoted context omitted.
> Being 17 or acting as part of a group don’t make you less culpable. Yes it does. Boys do strange things, boys in groups do stranger things, like not testifying against each other, especially if they feel society has abandoned them and the world is against them. Normal societies are set up to deal with that or prevent it. Fix your bloody society.
Sorry, but a 17 year old knows what it means to rob and murder someone and knows the difference between right and wrong. That’s the basic criterion for culpability.
First of all, if we are talking law and regulations: You don't know all of them and they are constantly shifting. And let's not get into the details of local legislation whether you live in a union of 50 or like me 28 states.
Secondly morals, those are learned first through your family then friends, school, maybe a religious community and later on experience as you master your life on your own. Or rather you learn from your mistakes or the mistakes others make.
The Supreme Court was right to disallow life prison for minors and your 18th birthday shouldn't be the hard limit for that.