I don't think that is true.
Do you have children? I've seen large families where all the children have the same "lifestyle", level of activity, and eat at the same table -- yet some just magically start getting obese at a certain age, as if a switch was thrown. Their genes, their body's blueprint desperately wants to be that different shape. It's sad, because you know it's not their fault, and that they will have to feel hungry at all times if they want to even fight it.
What form of gluttony are you proposing that "fat" child is guilty of? He doesn't eat between meals (praepropere), he isn't eating exotic food, he isn't eating "too much", just eating until he feels full LIKE YOU DO (don't deny it). He isn't eating like a pig in a trough, but eating in the same manner/speed as all the other children. And he certainly isn't getting his own custom plate of food prepared; he's eating from the same table.
So...once you've eliminated all the forms of gluttony -- how is he guilty of gluttony? You have to be specific.
The 5 forms of gluttony spells out the acronym PLANS by the way. This CI member should have re-ordered it; I would have.
Actually I don't always eat until I'm 'full' and sometimes I feel like I've eaten enough even though I can stil eat more. And if I wait about 10 or so minutes I can eat more.
You do not need to eat until you are 'full'. Also it's important to consider what full is. Some people think full as being completed filled to the point of not being able to eat anymore without being sick.
A person should eat based on either satisfaction or knowledge based off their weight/height.
Also different people have different metabolic rates. Even among families one boy may need 3000 calories to gain weight while another needs 4000.
Type of foods also matter. Meat makes me fill full much quicker than junk food despite being lowe calorie.