When are you able to go to KZ?

When someone hits level 70, almost the first thing they do is try to get into Karazhan. To do this you need to go through the various attunement quests and earn your way in. However with help getting attuned to Karazhan is very simple. So simple in fact that many (most?) people get keyed and then try to run the instance far before they are realistically able to be at all helpful there.

As with anything, there is no guarantee. You could take players that have much higher stats, but no ability to play their character in a group, and fail. Reversely, you could take several with lower stats that play their characters flawlessly and make the raid.

You can read all the details in our Minimum Requirements for Karazhan guide and then comment on it in our forums