Take a peruse through the FAQ section it should answer a lot of your questions and a lot more in depth than I can write out.
Age to attend games is *usually* 18+ (because you can sign your own waivers and whatnot). SOME places will allow 16+ with a parent or guardian signing the waiver however they're not really common to the best of my knowledge.
Take a look at the games and events section and you'll see. I don't know about over in the East so that's the best I can do. Field fees can range from $10-25+ (and big weekend milsim games might be $100 or more).
Startup costs are variable really. It *can* be done on $600 if you snag the right deals at the right times and are smart with your money, but comfortably it's more reasonable to budget $750-850. It doesn't have to be spent all at once but budget $450 to start with the bare minimum then another $200 over the next few months to get other gear you "need" like some sort of vest/chestrig, PB mask/goggles (assuming you rent/borrow from the field the first game), extra mags (a high cap is OK for the first game but you should consider getting mid and low cap mags later down the road), etc.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE