My older two took the SAT in 7th grade, age 12 or so. They took the 2400 scale format in 7th and again in HS, so I do not have any experience with the new format.
They understood that the SAT is a test for HS 11th and 12th graders, and that they wouldn't ace it. However, the test wasn't so difficult that they felt demoralized.
They both took the ACT in 11th grade (we are in an SAT area of the country), and while they would not have been familiar with all of the subject matter in 7th grade, there are a good number of questions a bright 7th grader could answer.
