Ill explain in a nutshell being a gun freak.
You can buy a rifle or shotgun at the age of 18.
You can buy a pistol at the age of 21. However, you can receive on as a gift or inherit one. Thus you may own a pistol before the age of 21 but you cannot buy one.

Carring purposes. If you have a rifle or shotgun in your vehicle before the age of 21 and without your concealed weapons permit you may carry it but it must be unloaded with the stock open. And generally the clip needs to be out of the case if the rifle has a clip. (I keep my 30 round clip for my sks in the same case, never got bothered about it)
Pistol wise. If you are under the age of 21 you may keep the pistol in your vehicle in plain site and the clip and pistol may be one unit. If the pistol is hidden you must have the pistol and clip in two different places of the vehicle. (IE, under the seat and the glovebox) The reason you are able to carry in your vehicle is a huge bi law thus stating your vehicle is an extension of your home no matter what. Your vehicle is privite property.
Once you are 21 and have the concealed license, the gun can be hidden, loaded, and chambered.
The big thing the cops will screw with you is where you drive with your vehicle with the guns. Your not supposed to be on school campus's or churchs or things of that nature. You can look those areas up. However, again that bi law thus stating your vehicle is your own privite property you may get away with it.
Personally I dont go anywhere, and I mean anywhere without a rifle in the truck or shotgun.
My .02