Hah this sounds way too familiar. Everyone is making such a big deal out of this.. trust me, it's not needed. I turned 20 about 2 weeks ago, and I had the exact same thing. To be honest, I don't know if it's the same case ofcourse, but I wouldn't get all too worried about it. My reason was that the change from being a 'teenager' going to 20 (which suddenly sounds like a lot more) was a bit.. hard to deal with. So I didn't celebrate, didn't want to see anyone, etc etc. because I considered the 'getting so old' (haha) part a negative thing and thus by far no reason to celebrate. If he has the same issue, then he'll be fine in a little bit. Don't worry about it. Ofcourse it's nice to atleast give him a gift, but you don't have to 'stick with him until you get to the root of it' because I'm about 95% sure there's nothing wrong besides what I just mentioned and that will pass. Nothing is more annoying than being bothered over and over again when nothing's wrong and you just need some time for yourself. Hope it helps. ^^ Congrats btw!