My parents are in their 60's and they don't eat much either. But they have definitely slowed down since they are both retired now. They eat two meals with a snack type of dinner. My dad is big in keeping logs of his daily intake and I think he is normally in the 1200-1500 calorie per day range. But he sadly does not work out and is pretty sedentary these days.
Personally I have a hard time eating more than 2,000 calories per day. I am normally in the 1,700-1,800 calorie range. I am super active and I do some type of workout most days. I am 5'10 160lbs and for some reason I can't eat more than I already do on a daily basis. I agree that if you are eating a lot of fat it keeps you satiated longer and you just don't get hungry. I have been doing a strict paleo diet for over 5 years now and my daily intake is pretty much the same since I started.
"If man made it, don't eat it" - Jack Lallane
People say I am on a "crazy" diet. What is so crazy about eating veggies, fruits, seafood and organ meats? Just because I don't eat whole wheat and processed food doesn't make my diet "crazy". Maybe everyone else with a SAD are the "crazy" ones for putting that junk in their system.