I think growing up as an overweight teenager/child has a much deeper affect on your emotional well-being than growing up at a normal size, then becoming overweight in college/20s. I'm not a psychologist, nor do I play one on television. However, I know that for me, being made fun of for my weight in middle school and even some in high school has scarred me.
Let's go back and revisit one of these such memories. The setting is a middle school cafeteria, tables are square or rectangle-ish and I remember sitting across the square from a girl named Jackie (and yes that's her real name and I will forever hate the name Jackie.) enjoying my lunch. I'm not sure what I did or said to provoke her, if anything, but I do remember what she told me. She said "Your belly is bigger than your boobs."
Some "fat girls" are lucky enough to have their "boobs" get bigger when they gain weight. Unfortunately I did not get that gene and have always been on the smaller side. I'm not upset about that, though. I was upset that the bia Jackie took the time and effort to tell me about it. Because of her I will probably always wonder if other people are thinking that same thought.
That's just one example of how growing up fat is different than getting fat later in life.