If you look at http://uesp.net/wiki/Skyrim:Draugr#Draugr page there is a list of when different levels of Draugr appear. Draugr wight at 13, Draugr Scourge at 21, Draugr Deathlord at 30 etc. Also different types of bandits are leveled.

How does this relate to leveled spells like the ones in illusion and restoration turn undead spells that do something like "turn undead up to level 13"? Would this spell always be effective against a Draugr wight because it appears at level 13, or does the player's level also have something to do with it to? Like if i'm at level 50 it won't work anymore for some reason?

This has never been clear to me. thanks to anyone that can answer it.

If the enemy is level 13 or lower it will work on them.