As a mage you can only wear very light armor. You can tell if you are high enough in skill for an item by checking the color of it's name. Also, when you right click on the item and examine it, you can see the amount of skill it requires to equip versus what skill you have.
EDIT - I should of mentioned that the color of its name works just like the con system. If its red, you can't wear it. It will also say at the bottom of its stat window that you do not have the skill required to use this item. If its orange or below, you can use it. If its grey, its time to find a new item :)
Edited, Fri Dec 10 18:41:26 2004 by Stashy