definitely research the laws so you make sure your safe legally.
there are state laws and fed laws, learn what you can on both.
even if you're not planning to concealed carry after you're 21, if you google the words "concealed carry" and your state - those sites found will have a lot of useful information on laws in your state.
briefly, to own a gun you have to:
- not have been declared mentally ill.
Having seen a psych over depression or some temporary issue is okay.
- not have a criminal record with felonies.
lesser crimes aren't an issue afaik, like nobody cares if you got caught shoplifting at walmart when you were 16. They care if you used a machete to rob a convenient store, or hack up your stepdad.
Handgun rules are stricter than rifle and shotgun rules;
if you want something for home defense and aren't 21, look into rifles and shotguns.
If you want something to protect you while traveling in your vehicle and can't yet get a handgun, find out you state laws on having a rifle or shotgun in your car. pay close attention what the laws say on "concealed" and "open carry", and "loaded" or "unloaded".
If you find you can carry a loaded rifle or shotgun, concealed in a vehicle, then you can look at folding-stock versions of such. NOTE the laws on loaded/unloaded and concealed/open, and rifle-shotgun/handgun vary state to state, and i've found the concealed handgun forums offer the most info on ALL the gun laws in any given locale, so even if not planning to carry and conceal, they are simply a good resource for info.