If you give him a higher level, it can be very confusing for players. If the player sees the wizard on 7lvl, won't he wonder if he accidentally came to some location too early? Level is a hint for the player whether he should be in this location or not it is too difficult for him.
CJMPinger has suggested that enemies could get a challenge rating instead of a level, and I really like that idea. Then you would only need a quick tutorial message explaining that level doesn't equal challenge rating, and that's that. But I get where you're coming from.
