The level requirements depend on the quest you've decided to take on. For Karazhan, you have to be at least level 68 or higher. The same often applies to other TBC dungeons and raids that require attunements to get access to.
To get all that top-tier loot, new armor, and the most sought-after Burning Crusade mounts, you don't need to spend all your free time leveling up. Instead, you can focus on your goals and getting some proper rest while our pro players will be working on the leveling grind. We'll help you reach the desired level in the shortest terms possible!