Don't get me wrong, there are things I'll consider "old school" in relation to today's standards, just to acknowledge the passage of time. I've been playing games for a long time before the original Alone in the Dark came out, but it was one of the pioneers of polygon graphics, a forefather of survival horror, and probably the template from which almost the entire genre is based. Yes, it's not "old school" in terms of comparing to the C64, which is my first computer gaming experience, but I feel it deserves the title. Also, just about any game, including those which venture into VGA territory, I might consider "old school" because they still use the text parser or SCUMM interface, which carries from the old-school tradition dating back to Zork, and probably further, but whatever. But the PSX being old school? I don't find that it truly deserves the title by any stretch. When I think of old-school RPGs, I think about games like Wizardry, the Genesis-based Phantasy Stars, even if they're not the oldest of the old, but they go back to before the RPG experience was 10 minutes of gameplay per 30 minutes of boring cutscenes.
Basically, I break it down like this:
Before the Commodore 64 and Atari, I consider my "pre-historic" stage, because they date back before I was gaming.
Even though it spans a few eras, anything from the Atari, C64, Amiga, NES, or PC games that still run on my Hercules Monochrome, no hard drive, XT computer are old school by default.
Games of the 486 to early Pentium era CAN be considered borderline "old school," based on certain qualifiers. Most of them, I do not consider old school in any way, but some of them defined an entirely new genre, and may pass as "old school" when taken in context of that genre. For instance, AITD, Dune 2, or 4D Boxing.