I know some people who do this in middle age, too. I wonder if it's a sense of 'fairness' that's been offended, a sense of helplessness that's triggered?
I have one young member in my family who would fall apart, even at 12, over some stuff that most of us think of as 'small potatoes'. I'd just be clear when these things happen-- give empathy, and let him express his emotions in healthy ways. "I know, it is such a bummer when he got more candy than you did, huh? That's just the way it is sometimes,and I know, I don't like it when I don't get what I want either." and then, give him some space to just move through that emotion and let it go. If he's not allowed to express his sadness, expect him not to continue to open up to you. Just give him some guidance--if he's really mad at home, invite him to take a break in his room and "come back when you're feeling better/able to use a regular voice/want to join us"..... it's a balancing act, giving them the empathy and support they need without allowing their upset to become the sole focus of everyone's attention.
Some things, too, you can let go of. He doesn't want to wear a jacket? "Well, bring it in case you change your mind." Empower him. Lost the soccer game? "If you know you played your best, that's all you can do. Sometimes, losing really stinks. The only way for your team to get better is to keep practicing."