How to stop gaining experience

How can I prevent my toon from gaining experience? I am Alliance and have found Behsten the Experience Eliminator in Stormwind Keep. I cannot interact with him in anyway. Is he bugged, or is there an alternative way to XP lock my character?

I re-subscribed to WoW to replay the classic instances. I have created a Death Knight which starts at level 55, and completed the necessary quests so I can begin classic instances. I completed several instances, which leveled my Death Knight to level 61 so I am no longer eligible to do classic instances. I have created another Death Knight and just completed the necessary quests, and am now seeking a way to XP lock this new Death Knight so I can replay classic instances.