Thanks Kasume, you underline my point.
My point is that most people normally define PGing as:
"Carrying out the same action repeatedly over a length of time."
However, they'll also argue:
"Without a certain amount of ability, nobody will take you seriously."
I have met very few people who chose to portrait them selves as "Apprentice" at their chosen skill set, for most cases people would like to be an "Amazing warrior" or "Quickest Shot". Since it is a game everyone starts with few skills, and their claims to those sorts of skills might seem foolish, but if they want to play that character they need to raise their skills... since your character creation isn't considered birth, you have history and should in theory already have some skills practiced, but this isn't really in effect (with the exception of language).
Edit add: By nobody portraiting themselves as apprentice I mean that most don't intend that to be their character, they say they are when they realize there skills don't match up with a master, but their intention is not to roleplay a apprentice.
Practicing something non-stop is not totally unreasonable. If you find someone extreemly passionate about something then they will (likely) want to train and practice at it as much as possible to be as good as they can. If people are disinterested they will probably not train (ingame or out). Think of it as your favourite hobby or interest. Do you spend a great deal of time on it? Probably. All night/day sometimes? Also probably, not always, but sometimes. If anything the complaint should not be that people "powergame" but rather that they stop after their skills have amassed, if they don't stop then they're still following that passion towards whatever they have chosen to devote their time to.
It is also important to remember that this is a game. It's RPG not just RP-Chat. Roleplay is of course necessary, but the end purpose is to have fun and enjoy yourself. As long as someone else is not infringing on your roleplay you shouldn't really try to infringe on theirs by saying what they can't do.
I understand it might be annoying that someone much younger game-wise is much more powerful, but if you're proclaiming yourself ingame to be an "amazing warrior" and then not training much and assuming you should be able to beat everyone, that's not exactly realistic either.
As Martin says, there will always be ways to maxamize skill gain, and it will be annoying to those who don't, but don't let it wreck your game! Online strategy games remind me most of this argument. Most of the number based web-browser games have strategies to "powergame" or maximize the gains and increases by following a set strategy. This does not mean you have to follow it, and may be annoying if you see most others, but it is within their rights to play like that.
As far as the powergaming subject goes... I am surprised to many people like to complain about powergaming while I see nowhere near as many complaining about "stat stacking". Stacking your stats all towards strength and such if you plan to be a warrior is a much worse thing than training constantly I think. How many people are actually born with subhuman intelligence, how many with no common sense (wisdom) and so forth... most people have some of each to varying degrees, and are not super strong and quick and nothing else.
Edit In Response to Damien below:
Having the GM create the character from the description and info given from the person might be the best, although I understand this is not possible due to too many people applying and not enough GMs to do that much work.
So all in all it is a very tricky subject I suppose, but I think it’s most important to remember that it IS a game, and people are able to play differently than you, even though you may not approve, doesn’t make it wrong.