Well, there's no way to be sure what led to his death without a reliable necropsy, at this point. If you plan to use it again, I would double and triple check your humidity gauge, it may have been malfunctioning and fluctuating wildly, if he was both having trouble shedding and portraying symptoms of an RI. I'm very sorry for your loss.

As to whether young snakes are more difficult than older more established ones, with the right conditions they should thrive. The weather fluctuations recently could have led to any of his environmental factors to decline rapidly.

Again, I suggest a necropsy, if you haven't already disposed of the body. It'll tell you exactly what went wrong and what to consider next time. He may have had something else going on that you couldn't see or help.