Two times in this thread I've seen the game fallout referred to as "Old school".
I haven't played fallout, but heard mostly good things about it.
Nevertheless, being in my 30ies, to me oldschool RPG (on computers) are the likes of Ultima Underworld (the first 3D RPG I've ever played. It was in old English when I was a kid not even understanding actual English and yet I spent hours on that game, not knowing what I was doing, still had fun. I could jump !), Eye of the beholder (Eye of the beholder II, same thing as above, a bit older, catching a few words here and there, but mostly moving my party and smashing monsters as I could), Might and Magic (I've spent a lot of time playing the III during the 2000, it was already old school then ^^).
I've played some Third Eye on table too at some point, it was funny too and "really" old school.
Ultimate hardware, your imagination
I just guess the meaning of "old school" varies from a person to an other. And staying vague they can catch attention if not backing.