I gave some weight-loss advice here: http://daved010.livejournal.com/208311.html?thread=927671#t927671
The whole comment-thread is here: http://daved010.livejournal.com/208311.html
It's mostly just a bunch of common sense, but we all know that common sense is never common, and rarely scented.
I was thin as long as I can remember, and I never seemed to gain weight until after I was 30 years old. I was 120 pounds, and 5ft8, just a bit thinner than the low end on the ideal weight charts. Then the pot-belly started forming. By 40, I hit 135 pounds, and I needed bigger pants and a bigger belt. So I started watching what I was eating, and I'm staying around 125. A few weeks ago, I finally got down to 120, so my diet goal has officially been reached, even though that one weighing was probably low due to dehydration.
I seem to be following the same pattern as my dad. He wasn't able to bulk up for playing football when he was young. After age 30, he started putting on weight, and now he has to watch what he eats.
The ideal weight charts are based on mortality rate. Small people tend to live longer (like the stereotypical "little old ladies"). But many illnesses cause sudden weight loss, which can be fatal in people who have no spare weight to lose. For me, 125 pounds seems to work.