I respectfully disagree that "old school" is being inappropriately used -- at least in proper context.
("Call of Duty 4", Gamespy's Game of the Year)
("Metroid Prime," Gamespy's Game of the Year)
("Myth: The Fallen Lords," Gamespot's Best Graphics pick for the year)
("Street Fighter II" on Super NES, one of the year's biggest hits)
("Legend of Zelda," American release)
("QBert" in arcades)
Space War (not embedding due to image resolution)
I am 30, and I virtually outlive modern video games. The outside edge of "old school" for video games is 30 years old. Look back 15 years, or even 10, and you wouldn't be able to believe these games were cutting-edge if your only metric was what's commercially available today.
This is why we can talk about older games as if they're relics from our grandfather's generation: because, in game years, they are. If civilization developed in the same time scale as video games, then firing up an emulator and playing an old Super NES classic would be like talking to someone who was alive in the time of Jesus. Sitting in front of an Asteroids arcade machine would be like shaking hands with the hunter-gatherer who invented bronzeworking.*
I would say the "modern" (new-school) video game era began sometime around the Playstation's success in the late 1990s; that was the time that the real transition from 2D to 3D took hold. "Old-school gaming" properly refers to the previous era, or (the sometimes newer but excellent) games designed under those principles. And it's pretty easy to see not only the graphical difference but the design difference if you've played both old-school and new-school video games.
P.S. Feeling old now.
* And the board game "Monopoly" would be a literal Neanderthal, walking in circles with his little dog while the rest of us are building cannons and cars.