please, god no! I hate that in other games! "sweet, I got new armor!"*tries to equip*"you need to be level X to equip this armor" then it just ends up sitting in my inventory for a few levels, and by the time I've reached the level needed, I've found something better.
They could use FO:NV's method, which had a skill/strength requirement for guns. If you did not meet this your gun would wobble around, reducing accuracy, and you would reload slower I believe. This means there is still a skill/level/X requirement, but it does not stop you from using it before you reach it.
But Oblivion already kinda had something like that, with the armour rating effectively equaling out to the % of the effect you got (i.e. AR of 85 at skill 100 = AR of 85. But at skill 50 = AR of 42). With that said, maybe something a little more complex would be better, where you only need an armour rating of X to get the best out of a lower tier piece of armour. Like a skill of 20 = max AR from Iron armour, while you would only get 20% of the max AR from Dragon Bone while at skill 20 etc.