I just point out that everybody knows that processed food is bad for you and contains very little nutrients. Mostly what you are doing is cutting out processed foods. Most of the foods you are cutting out are obviously bad like fries, cake, burger buns, soda, white bread, etc. Emphasize that compared to other kids, you are eating healthier than they are by eating fruits, vegetables, nuts, and meats. Therefore, the only real points of contention are that you are eating more meat than they would like and you are eating less grains. But try to focus on the positives and areas where you are doing better than most kids your age, even if they disagree with a few things. But it's still way better than eating burgers, fries, and a coke! I other situations, if you are young and healthy, it probably won't hurt to eat a few bites of rice or a potato now and again. Paleo need not be about total elimination. It is also about balance and shifting to more healthy eating in general. Now that you know what foods are healthier, try to eat more of those is all. YOu will still be lightyears ahead of most kids your age.
As for college, I went to UCLA and no one ever REALLY bothered me about what I ate. I guess you might get some friendly ribbing from time to time. SOmetimes people would get a tad of ribbing for eating super healthy and sometimes people would get a tad of ribbing for eating super unhealthy. But nothing serious. THey may not even really notice that you are not eating grains. We had plenthy of foods to choose from including a salad bar and meats. WHole potato was often on the menu as it is super cheap. There was always fruit. If the meat is breaded, you can always pull the breading off. I actually used to do that a lot even though I wasn't paleo back thne. It would have been fairly easy to eat paleo when I was there. Even if there are a lot of vegans, it's not like they are going to make up a majority of the eaters. THe rest of the kids will want meat and the school will provide it.
In college, you are basically free to do what you want as long as it's still legal. The hard part will be going back home afterwards and having to face all the rules and nagging of your parents once again! ;-P -Eva