Well... of course I'm an old man. So I suppose that makes a difference. I'm about 5'8" & weigh... oh... around 135 pounds. I've been at or around that weight for many years now. I don't get a lot of exercise... mostly just walking our dog. But, over the years, I sort-of learned what I can & can't eat. I have a bowl of whole-grain cereal for breakfast with a banana or some berries & then I eat dinner (no lunch.) I also pretty-much always have a dessert of some sort during the evening because I have a sweet tooth.
But, beyond that, I rarely snack. And when I do, it's just a few unsalted mixed nuts generally. I also seldom eat out at restaurants. I think not snacking & not eating out are the keys to my being able to maintain my weight over the course of many years.