I'm in my mid 20s, and I started doing this when I was 13.
Quite often, if I'm stressed or angry, I'll skip meals because I just won't feel like it. If I've screwed up, I'll punish myself by not eating.
If I'm angry with someone, my way of sticking it to them is to not eat. It's kind of me being spiteful, like "that person is angry with me therefore I'll hurt myself".
There's probably little logic to it (!) but for me, it's a form of taking back some control.