I was the same way.... I got up to 235 at age 17 (6' tall, medium build) before getting fed up with being fat. Obesity runs in my mom's side of the family... so maybe genetics did play a role, but mostly I just ate like crap. I bascially starved myself like you and lost 75lbs within a year. At that point, I weighed 160, which really is my ideal weight. However, I had lots of loose skin and I still thought I looked fat, and I think I developed sort of a mental complex about weight loss, perhaps some mild anorexia. I continued to lose weight through light eating until getting down to 135lbs, which I maintained until I was 26. At that point, I got in a motorcycle accident and my weight plummeted to 119 lbs. My doctor put me on antidepressants and threatened to feed me through a tube - so I reluctantly ate lots of food and gained weight. I held steady at 150 for a couple of years, then my metabolism began slowing, probably due to age, and my weight crept up to 175. I started cycling a lot last year and lifting weights and I'm now holding steady at 160.

I stick out like a sore thumb at family gatherings because I am at the correct weight.

I think that genetics plays a role in predisposing people for weight gain, but in the end, it's up to everyone what weight they want to be.