Discuss Sad Gramma's answer to: Question about the movie Nell

I understand that a person must acquire language by the age of six to avoid being "mentally retarded."  Nell, however, learned language at a very young age even if it was not language as we know it, as she and her twin communicated very well.  I'm no psychologist, speech therapist, or behavior specialist, but I would think that her intelligence potential, despite her ignorance of school-taught information, would be intact.