I'm sure a staff member will come along and correct me if I am misinformed, but I'll try to answer your questions as best I can until then.
If I understand the current rules, you can play, without guardian supervision, at 16, but you need a guardian to sign a form saying that you can play. Said form is available for download at this link:
https://alliancehq.files.wordpress.com/2014/12/legalrelease.pdf
As for safety, Alliance LARP has been deemed to be safer than Little League Baseball. That doesn't mean it isn't smart to take a few precautions. My recommendations are:
-Bring and use plenty of sunscreen to avoid sun burns
-Wear sturdy boots that you have worn long enough to be comfortable in (to avoid twisting your ankle)
-If you wear glasses, wear one of those sports bands that hold them to your head
-Bring and drink plenty of water to avoid overheating
-Practice safe weapon combat with an experienced player before the game if possible (if you show up before game starts, someone on staff or an experienced player will almost certainly be happy to help you with this)
The community is very helpful and you should find plenty of support during your first game. Take advantage of that and you should have little difficulty staying safe and should have a good time. It is very unlikely that you will be injured, but if it should happen, game will literally stop to ensure your welfare while on-site medics see to you. If necessary, you will be brought to a nearby hospital (though such occurrences are extremely rare). Better safe than sorry, make sure you know your insurance information just in case.
-MS