Before I say anything, I'm a native speaker and went to French school my whole life. Here are my score, as they might give you an idea.
CE (Reading): 283/300 - C2
CO (Listening): 336/360 - C2
EE (Writing): 398/450 - C1
EO (Speaking): 447/450 - C2
So...
To all applicants who want to give TEF a shot, as I've stated in another post, it is definitely NOT an easy test, even for native speakers. I truly wonder how they expect anyone who hasn't been speaking the language for years get a good score. For instance, when you take the IELTS, any complicated vocabulary will have a star pointing to a footnote. There you will find the meaning of the words. In TEF, not only do they use idioms and advanced vocabulary in both reading and listening, but they're also not defined for you. Hell in some listening conversations in my exam, I heard some borderline slang terms!
If you've been speaking French for quite some time, by all means go ahead, as it may increase your CRS score. If you're just picking up a book, you're preparing yourself for a world of frustration.
Sadly, not only will you not be able to learn it in 6 months, unless you're Rain Man...but also knowing the language is one thing, and scoring well on TEF is another thing. Above are my score after 18 years in french school, and absolute daily usage of the French language.
I hate to break anyone's dreams, but just like the very first post in this thread says... we need to be real.