Yeah, an out of state permit MIGHT work, but I'm not a lawyer. You also might be able to get a permit early if you have good reason. I've heard of that. Kind of like how 12 or 14 yo can drive trucks in NE. Has to be a truck though, and for farming purposes, but they drove to school. Funny seeing elementary kids driving to school, but it is common out in the prairie.
Dude, I know how you feel. The main reason I carry is due to the fact that when I was younger, I was on the receiving end of a lot of violence. I've been held at gunpoint a few times, and beaten by ten guys, barely survived, went and knocked on a stranger's door and one of them came back to finish me off (he had his hand down the front of his pants coming accross the road and he was alone) but the guy that answered the door aimed a double barrel at the dude and he took one more step to dare him but the hammers being locked back did the trick. Had he not answered, I was going to break the door down and probably would have been shot myself. I was cornered.
It is horrible that in some instances younger folks can't be armed. Exceptions should be made for circumstances like yours, but a lot of people don't quite get it until they've been in our shoes, so you get a one size fits all law. For the most part, 21 isn't a bad age for CC.
If you have a bus, I'd look into that. First thing you should do though is call a lawyer. Goldman or Goldberg, he does NFA trusts in FL and he knows firearms laws inside and out. He's the big reason trusts are popular today. In case you didn't know, lawyers offer free advice over the phone, a lot of folks don't take advantage of this, but you should. If there is a loophole, that guy will know about it for sure.
I'm in my 30's now, I carry all the time, but now for some reason I'm not such an appealing target. When I couldn't carry, I was constantly in trouble, but I also grew up in the South which is in my experience a much more violent place than WA, where I live now.
Pepper spray may be your best bet. Nobody will advocate you breaking the law on here, but truth be told, I had to do it myself. This was 15 years ago, so statute of limitations is over and I live on the other side of the country now so I feel safe talking about it on here. The third time being held at gunpoint and surviving that beating (cops said it was a gang initiation and that I was supposed to be killed, that they screwed it up) was enough for me to say screw it. Oh yeah, and while I was being beat, at least one cop drove right by it and didn't do a thing until called. Your safety and life is in your hands and only you can make that decision. That the government has put you in a catch 22 is unfortunate. Still, my advice is to call the lawyer and see if there is a way around it.
Last thing you want to be caught with is a concealed weapon between the ages of 18 and 21. The consequences could be such that you can't carry ever, in FL anyway. But that is a decision you have to make for yourself.
Finally, if they want to be @sses about it, you might be able to get away with carrying a rifle in public. Not sure about how you have to store ammo, likely it has to be unloaded. But you can get rounds in a bolt action pretty quick and folks aren't inclined to mug people toting rifles around. Still, call the lawyer to see how this works and where you can carry it. That stupid school zone garbage can be an issue if you have to go anywhere near one.
Good luck, be safe, and know there are folks that know where you are coming from. Now go find that lawyer I mentioned and give him a call. Look up the name on Google along with FL and NFA trusts, you'll find him.