Basically and I am by no means expert only been playing a few years myself. There are two types of full face protection you can buy there are always risks and advantages and disadvantages no matter which option you decide choose:
Mesh Masks: These are masks that have tiny holes for you to see out of, but small enough so that BB's cannot enter an example of this would be a fencing mask http://www.zerooneairsoft.com/product_info.php?cPath=287_438&products_id=7272 or you prefer a mesh mask http://www.zerooneairsoft.com/product_info.php?cPath=287_438&products_id=2439 these are very common for starting airsofters as they are cheap and effective
Glasses Masks: As you are under 18 youll need a full face glasses mask which fog up like crazy no matter how much anti fog you apply to them. There are easier to see out of though (debatable) however fog tends to ruin my day heres an example for you http://www.ebay.co.uk/itm/Paintball-Proto-Goggles-Switch-EL-Black-Paintball-Mask-UK-SELLER-CC1-/271177017874?pt=LH_DefaultDomain_3&hash=item3f2368ea12
Please note these are just examples you will have to do research on which masks have protection for your eyes, no sport is worth loosing your eyesight so be sure you are buying a worthwhile official product. Dont let this scare you though ive been using mesh masks for years. Just do your homework if its glass ensure they can withstand the penetration of a bullet