I am not sure what you mean by an earlier age than what it was designed for. The Talent Searches used Explore as early as 3rd grade. My third-graders took the Explore through C-MITES at age 8. It was not too early and neither of them were overly stressed, even my relatively worst test-taker. Of course, I did not prep them other than have them try the sample questions and I did not make a big deal out of the test. Having said that, you need to base your decision on your child's mindset about difficult test and perfectionism. DS could not care less and raced through the test, spending a considerable amount of time twiddling his thumb at the end of each section. Although he scored in the 99th percentile (except in English) compared to other 3rd grade Talent Search participants, he by no means hit anywhere near the ceiling. DD actually cared more and could not finish a single section and left a lot of questions blank. I forgot to remind her to save a few minutes at the end to guess. However, I simply told her after the fact that it was no big deal and she didn't worry about it. Interestingly, while her scores were much lower than DS' scores, a couple of her scores were actually in the low 90's percentiles compared to other 3rd grade Talent Search participants.
The Explore report actually compares your child's score to nationally normed Fall 8th Grade. However, I don't think that it would be useful as a measure of achievement. I know that they categorized it as an achievement test, but I really think it is in large part a reasoning type test. Notwithstanding their scores vis-a-vis 8th graders, neither of my children is anywhere near ready for 8th grade. I think for your purposes of homeschooling assessments, you are better off using actual end-of-year assessments corresponding to actual school curriculums, which will likely have higher standards and more expansive contents.
