For the youngin' situation:
If I were you, I'd flip the polarity on a few mics or turn up an aux send to the monitors so something starts to feedback - keep that boy on his toes! There's nothing wrong with a little pride-bashing, is there?
I'm 22 and know that I don't know everything. I am confident in my abilities, but am also willing to admit my faults and learn from those occasions which go badly. THAT is this young person's issue, methinks - he is not willing to learn. That is the reason I say play around with him - it's very sobering to have stuff blow up in your face when "you know everything".
For the old-timer:
Let him know that his first responsibility is to serve the congregation using the talents God has given him - that is why we do what we do in our various churches, isn't it? It's something we are gifted in (hopefully). If he is focusing on his own agenda, he needs to rethink his position before you (or the person in charge) does it for him.