It looks like there's a pretty even number of people on each side of the pistol/rifle dividing line, and I get the impression that you are thinking of the going with a handgun. I love hand guns, but I don't think they are a very good choice for a new shooter. So far, all of the suggestions have been great (which is to be expected on THR) but there is one thing that really stand out in post #1: This is going to be the new shooter's gun, not a gun for the OP to take the new shooter (NS) to the range with, so the NS is going to have to be able to buy ammo and transport the gun on his own. Also, the NS is 18. I'm not sure whats it like in Florida, but around here (WA) you can't buy handgun ammo until you're 21. Some places have refused to sell me .22 ammo because they make handguns chambered in it
It might be a good idea to include a few bricks of El Cheapo .22 ammo with the gun.
Again, I'm not sure what the Florida laws are regarding the -21 age group and handguns, but I think that the rifle is going to be a safer option from a legal standpoint. It may be legal for him to have a gun in his car if its locked and unloaded, or whatever other restrictions the state places on you, but all it takes is one slip up, one incident of forgetting he had the pistol in his jacket pocket because he wanted to try carrying around the house, and he could lose his 2A rights for a long time. He probably will follow all the rules, but its still possible for a tailgate to be out, and the officer that pulls him over is not as competent as he should be, and the NS is in for a much more interesting outing than he had planned on. We all know that the NS would be in the right, and the charges probably wouldn't stick, and this probably won't happen, but is it worth it? (I'm not suggesting that you should not exercise your 2A rights to the fullest, just that it is not always the smartest thing to do when just starting out. Think of it like situational awareness: just because we can go to the bar that the local paramedics nick named "Stab City" does not mean that we should) Unlike many of the members of this board, the NS will not have the benefit of a CHP or CPL or any other piece of paper that helps prove he is a "Good Guy." Theres also the very real possibility that he will get pulled over just because he is young, and that the LEO's, or anybody else for that matter, will be less understanding due to his age.
IMHO, one of the best guns for a new shooter is a .22 rifle. I think the Ruger 10/22 is a pretty good gun, but so are some of the bolt action rifles on the market. I've heard good things about the Henry lever guns, but have never tried one. I would look into a gun that is not a semi-auto for two reasons; He will get more out of his range sessions because he has the added action of working the action, and people will be less likely to jump to conclusions about the reasons that he bought that type of gun. When I was 16 and getting into shotguns, I had narrowed it down to a Benelli Nova, a Remington 1100 and a Remington 870. The 870 had wood furniture and looked more like a sporting gun, while the other two could best be described as "Evil Black Shotguns." I know its not that big a deal, but to an uneducated observer who wants to stick it to someone that he sees as representative of those "Punk kids that don't stay off my lawn," well, theres a reason why I picked the 870.
If you do go with the handgun, I would recommend staying away from the autoloaders. I don't like guns with a whole lot of controls on them; theres little more embarrassing than standing at the range while people watch you try to figure out how to get the gun out of slide lock (In my defense, it was the first time I had shot a handgun.) If something goes wrong with the auto, it can be intimidating, especially to a NS. Revolvers are fun, and you don't get frustrated trying to load the magazines. There are a lot of aspects of shooting that most of us take for granted, because we have earned our experiance, our knowledge, and our skill level. A NS won't have any of that, and I think that its better to give people the best advantage when they start out, and then let them progress to harder things, instead of letting handing them an AR and saying "Have at it." Revolvers are simple, reliable, don't evoke the gang-banger stereotype that us young people have to deal with, and are pretty fun.
My opinions are just those, opinions. My shooting experience is limited, and most of my post relies on what I have dealt with, or what I have felt anxious about while driving to the range. My opinions on teaching come from one summer teaching archery, another summer teaching a crash course in paddling to people renting kayaks, and a little over two years of teaching kids how to swim. YMMV.
No matter what you choose, I'm sure he will love it.
Chris "the Kayak-Man" Johnson