Thanks for the chapter!
He looks and acts more like he's 16. Besides, isn't 20 a little late for learning fundamentals? I get he's a demon, but unless they're like Elves that live for a few centuries that's really late. I bet Gelde was more scared than disgusted considering the MC was able to shake his arm up and down like that despite him trying to hold it still. Sheesh, seems like humans aren't the only ones to bad mouth someone just met based solely on appearances. In any case, MC has definitely broken the device and likely to have taken out the cream of the crop from it exploding and shooting shrapnel all over while completely missing him as he had the wits to duck under the pedestal in time. Also, teaching staff shouldn't have assumed everybody knows what a dungeon is or how to use it so should've given more info other than can make/destroy/repair everything created in it and are going to be living in it.
@Spooder9 What's there to be scared of? It's just the usual trope of the MC completely destroying a priceless and irreplaceable artifact by accident just from touching it. That and forgetting to wash his hands first. After all, cleanliness is next to godliness!