Originally Posted by Drithius
Different areas within zones are locked in at a particular level. Even if your stated 50 wizard were to journey to a newbie area, (s)he would only be level 3 (or there about); similarly for other, more advanced areas. You still retain all your unlocked skills, but you're considerably less powerful with them.
It's frankly about time another MMO beyond City of Heroes implemented this great mechanic. Not only does it mitigate griefing, but it's far easier for people from all level ranges to help one another.
Bear in mind that your example also plays into a (fallacious) mindset that the game is about "killing things" for experience. That tired old game model is very much minimized in GW2 - most of your experience stems from dynamic events and heart quests, for which any contribution is rewarded collectively amongst players.