I'm pretty sure mages can't dual wield, as far as I know the only dual wielding classes to date are; Hunters, Warriors, and Rogues. Hunters and Warriors get their dual wield at 20 while Rogues get theirs at 10, hope this helps.
Dual wielding weapons is pretty cool to look at. Hunters look bad *** with two axes, warriors with two swords, and rogues with two daggers. They are three different classes but they do have something in common: Melee. A mage wouldn't focus on their physical capabilities because they've conditioned themselves to harness a power that is intangible. I highly doubt mages will ever have dual wield as it would be a waste of a proficencey. Stick to watching your enemies scream in unimaginable pain with your spells and forget about making them laugh with your twin feather-dusters of doom.