Get it Here

Guys don't grow out of huge appetites unless there is a medical reason to do so. While it's true that metabolisms run fast at a young age, they don't just slow to a stop in a year or two. I would think that if Justin had a large appetite at 17, it would still be there when he was 22, or 24. Just because we don't always see him eating, scenes like the spaghetti scene in the birthday episode show that he can still put it away.