old school is a feeling. you can buy a brand new RTP Viper or chplinstone lever action that is entirely "BRAND NEW PARTS" but is it old school? now, its has less age than a B2K that is pushing 14 years old.
though i generally despise the term, old school is a just a way to approach the game, when you aren't buying the latest or last years new stuff. you could say that old school is just using old guns that no longer have factiry support, or are being made.