Eating Disorder

Not true. Boys and also older women can get them, but those cases are rarer.

I think one reason it could be more common for teenage girls is that their bodies change significantly in ways related to weight when they transition to adulthood from childhood. Breasts, hips. (Boys tend to just grow, without necessarily putting on more fat.) It's startling and uncontrollable and some girls react to this by trying to control things by severely curtailing their calories.

I'm sure it's much more complicated than this but that's one difference between boys and girls I thought of immediately.

My thoughts are that in our society (in fact, most societies), young women are evaluated on their appearance, while young men are evaluated on size and strength. Later in life, people accumulate other accomplishments, but early on it is how you look. That is why boys hit the weight room and girls hit the diet books. I had a great friend in high school, super honor student, lots of acedemic success. Her brother was 6'4", 250lb, line backer material. She was 5'10" and of solid build (clearly the same genetic stock), although I never thought of her as fat at all. After senior year and a messy break-up with her boy friend, she started losing weight. I was one of the only two friends allowed to visit her in the hospital. She was down below 90lbs. Way scary. I'll never really understand the pressures that produce that kind of behavior. Guys just don't see that.