The only thing I can think of is a Denny'* grand slam breakfast years ago. When I went to Chicago this past July I did eat a whole slice of deep dish pizza (Giordanno'* = yummy!!!) I was so stuffed! Then the next day I tried but couldn't finish a gyros.
I'm just a scrawny old chicken legged 140 lbs but I agree that I used to be able to eat a whole lot more than I can now. I remember eating 12 hot dogs once.
I think it has something to do with the elasticity of a younger stomach.
Either that or the accumulation of too much fat around it, restricting its growth.