Some Juveniles who commit serious crimes such as murder can sometimes be rehabilitated however some Juveniles may not be able to rehabilitated and need to stay in prison to protect society.
So I would say that yes it should be legal to give Juveniles Life Prison Sentences but I also think that they should be given a chance to see if they can be turned around and get back into society.
Sometimes Juveniles are not thinking of the consequences and do stupid things and sometimes they regret doing it or do it anymore.
So I believe that the Juvenile should be given a life prison sentence for something such as murder but also should be given the chance after 5 or 15 years in prison to be able to get back to society as long as they are able to get back to society.
But some people just never change and deserve to stay in prison.