As a kid on the exchange system, I remember hoarding and hiding candy. And my A1C definitely suffered when I went to college and learned to eat what I wanted and suffer the consequences (not quite as bad as some of the other posters above). But I had A1Cs in the 8-9s for years until more recently when I stopped to focus on it. It was "good enough" and let me not have to be so vigilant.
The other big impact of the diet as a kid was that I grew up with a paranoia about food. I have trouble sharing food as an adult because I still have that exchange mentality in my head. I remember in high school a classmate taking one of my lunch components and I panicked because I knew my day was planned around me eating that exact, full, lunch. So now, I always have snacks on me and do not pass them around the table the way other people may do, because I don't know if I may need them later (even though I'm on the pump, have a CGM, plus access to money and vending machines).
These days, however, as an adult with a Dexcom, I've certainly figured out which foods are more problematic than others and have made decisions. Prior to going low carb and getting pregnant, my two foods that I wouldn't give up was Friday pizza and ice cream. So, I did troubleshooting after troubleshooting until I figured out how to minimize the spike. I've long since forgotten the formula, so I'll have to figure that out again if I choose to reintroduce those after the baby comes, but it involved pre-blousing, multiple staggered boluses, and a temp basal for a set amount of time. Still a lot of planning and sticking to a consistent amount of those foods, but it allowed me to enjoy the foods that I liked the most.