First off, get Age verified, you're 18. That makes things 100x easier.
For your questions..
Guns --> AV section.
A paint ball mask is totally fine.
Two types of airsoft --> Milsim, and casual
Milsim's are realistic, longer, objective based games with restrictions in terms of kits, guns, ammo, those sort of things.
Casual games are usually short objectives, or just run and gun type elimination games in which any tactics work. Whether you're a hard core milsim, or a once a month, come in jeans type of player, you'll have fun.