That’s not really implied by simply acknowledging that their brain isn’t developed yet, not sure why you are defensive about it like giving them keys to a death machine when they also clearly have had mental issues and haven’t gotten far along in their prefrontal cortex is a necessary rite of passage. There are a lot of possible angles to look at situations like this to consider how to fix them and blaming the people involved might be the easy answer but actual justice for society becomes more complicated. Nobody wants to deal with this story, and that’s the bottom line.