It’s extremely nuanced. ‘Light years ahead’ is correct since you are thinking about a race where one competitor is a long distance ahead of others. On the other hand, ‘light years away’ doesn’t make sense, since we think of achievements in terms of time needed, rather than distance.
I’m an adult and am not responsible for anything you described. They were all there even before I was born. In fact, the same may apply to my parents or even grandparents. I’d rather blame a sociopolitical class than any single generation for all those ills.
But to answer your question, yes, I’d blame that entire class for the harm caused by young people using murder tools they introduced. They did it with the full knowledge of its consequences. They valued momentary material gains above the wellbeing of entire generations. They absolutely should be punished for all the mass shootings in schools, because they knew it could happen. Yet they chose the blood money. Similarly, if an entire city is under a drugs epidemic (like the current opioid crisis), wouldn’t you want to hunt down the producers and suppliers, instead of the users?