[L473ncy]

16+ (in SOME cases, usually it will be 18+ however) If 18+ age verification can be done at the field if there is an AV rep present (ask first to see if there will be any attending, there usually will be).
A gun (or at least asking around for a rental/loaner beforehand)
Field Fee+gas money if carpooling ($10-25+)
BB's ($15-20 for a bag of BBBastard, AirsoftElite, Madbull or similar if you can get at least the .25 gram ones if playing outdoor (note you will chrono with .20))
Mags (single hicap or a few 120 round midcaps will be fine, I also hate to say this but it's OK to store them in your pocket for now until you decide for yourself if this is for you and you want to spend some more money)
Boots ($80-150+, hiking boots are fine and what I use, when you decide to spend more money you might think about getting your hands on some military boots)
Eyepro ($30-80+) Cheap paintball goggles/masks can be found at places like Canadian Tire but a pair of JT Flex8's will run you I think $60-80. Otherwise if it's a paintball venue you're playing at they might have masks for rental for like $4-5.