I have always been like your son, I can eat a seemingly limitless amount of food and not feel full. I was obese by 4th grade and stayed that way until I was 35. I truly believed that I was simply genetically programmed to be obese, after all my diet was healthy and I was active.
But lo, one day I decided to start tracking my diet and activity levels and I found that I was consuming more energy than I was expending! I started to eat to my energy requirements and AMAZINGLY I lost 80 pounds over the course of a year, and leveled out at a healthy, sustainable weight. I never felt hungry, because I was eating to my energy requirements, not to my appetite. I still love to eat, but have learned to stop eating once I know I've eaten enough to fuel my activity. Usually after about 15 minutes my brain 'catches up' with my stomach and I stop feeling the urge to continue eating.
I'm teaching my daughter to do the same. She, like me, loves to eat. there's nothing wrong with that. Eating is very pleasurable! But being obese is physically uncomfortable and restricts movement. Moving is fun too, when your body is strong, healthy and not carrying around excess weight. There CAN be a balance, and I suggest that finding that balance is better than feeding one impulse (appetite) at the expense of the other (activity)..