I'm pretty sure that there is going to be 22. Cause that would be insane. They can't wrap up a series like this in only 18 episodes. I don't think JJ would do something stupid like that. He already made the mistake of "killing" Vaughn.
So I'm almost certain that there is going to be 22. What you all read was probably false information. Don't belive anything unless it comes from a pretty reliable source. (ex, ABCMediaNet, Kristin, Ausiello)