I'm not sure about that one. The Anime has changed the meaning of the term over time, and I fully expect it to be changed again at some point.
But if I had to guess, I'd say that I don't think there is an official pre-requisite for becoming a Pokemon Master in the Anime (aka there's no set guideline). Because if there was, then the process to become one would never change. But the term does exist in the Anime, and it's used to describe several supporting characters in the series. And as has been illustrated before in the series, the process has indeed changed, at least at a glance.
But has it really? Has there ever been an official list of things required to become a Pokemon Master in the Anime? The short answer is, no. There hasn't. All we ever know about the Pokemon Masters is what they've done, not what is needed in order to become one. Ash aspired to become a Pokemon Master in Episode 1. He wanted to catch every Pokemon, win the League, AND become a Pokemon Master (implying that catching every Pokemon, winning the League and becoming a Pokemon Master are indeed three completely separate things).
Plus, whenever you hear about a Pokemon Master, you always hear about what they've done in life, separate from them becoming a Pokemon Master. Cynthia won the League, defeated the Elite Four, AND became a Pokemon Master. She didn't win the League and defeat the Elite Four TO become a Pokemon Master. Implying once again that becoming a Pokemon Master is a separate task (and possibly also implying that battling the Elite Four might not necessarily be directly connected to winning the League in the Anime; but I digress).
With all that in mind, I imagine that it's more of a formal title, akin to being knighted or inducted. There's really no set pre-requisites for becoming one. You just do extraordinary things, or accomplish enough tasks, and you're eventually recognized as one by the guys in charge. It's probably supposed to be the sports equivalent of being inducted into the Hall of Fame. They don't just look at one thing you've done, but all of the things you've done over the course of your career.
Last edited by SBaby; 7th April 2013 at 11:50 PM.
Rules of fansites:
1 - You can either be right, or you can be happy.
3 - If you think someone is lying about being an expert, they are.
5 - If you think someone is lying about knowing people who work in the industry, they are.
14 - All sources are one-sided.
27 - There's no such thing as an honest politician.