Twinking is making an elite (often for PvP) character. thats why it would be 19,29,39,49 etc etc... anyways it will usually invole getting awesome gear,good enchants, and various other EXPENSIVE and not easily obtained things. dont bother twinking if you're new, only make a twink once you have a decent lvl for the money (getting your guys crusader and rare world drops is hard as heck lol) anyways......... I personally dont have a mage but go fire..........maybe ice............wait for arcane till a decent lvl if thats what you want......but it is personal choice with the builds.....if you are gonna solo stuff alot i would go ice if you wont have people with you when you do quests and stuff......fire if you will be in groups....and arcane.........i'm not sure why...
anyways hope i helped and good luck with that!