I think it has to be a case by case basis and is highly individualized. There was a 13 year old that killed a young neighbor boy because he just wanted to know what it felt like. Had no remorse, no emotion, etc. He should never be released because he is not ever going to be rehabilitated. You cannot fix a true psychopath because they do not develop a conscience the way most people do.
However, kids that can be potentially productive members of society one day should not have their lives stripped from them at such a young age. They can learn and possibly be rehabilitated. There is a fine line here and it really depends on the case and the individual.