I'm 52.
5'9" and weigh 168 lbs. Not an ounce of fat - and yet I eat like a frickin' horse. No diets.
I'm the annoying one at family get-togethers - everyone looks and wonders how I do it.
Naturally high metabolism. And I stay active constantly. Mountain biking and trail hiking in the summer months - rough terrain that requires good physical exertion. Turn off the TV, step away from that fat-inducing gaming console...and just go do something. A lot of people don't realize how sedentary they actually are.
And then they wonder why they're fat.