Cool!
Actually, one could say the original 1e AD&D Bard class was the original prestige class, so the concept goes further back than 3e. But it was much, much harder to become a 1e Bard than it was to enter any of the 3e prestige classes.
Viewing post in Prestige Classes for Basic Fantasy Roleplaying Games comments
Unlike sub-classes, Prestige Classes weren’t tied to a particular base class. Instead, a character had to meet certain requirements. For example: to become an Arcane Archer, a character had to be an elf or half elf and meet a minimum to-hit bonus. They didn’t have to be a fighter. I can’t remember if druids began as a sub-class of cleric or if there was an independent class version in Dragon magazine but the game’s approach to some of the extended classes had some twists and turns before they settled down.