I would doubt that a college would be THAT interested in the score of an 11 yo- if the 11 yo got an 800 math and then at 17 got a lower score, that would look bad. If they get an 800 at 17, great.
If a kid did very well in SAT (e.g., meeting SET requirements) under 13, it raises the expectation of admission officer. I feel that the kid need to have significant follow-through in high school years, like doing well in AMC12, AIME, winning Intel award, Davidson fellows, etc. Verbal kids have less opportunities for national recognition, but winning some writing awards would be good. On top of that, the kid need to follow-through with a perfect (or near perfect) final SAT in the junior year.
It is just some extra pressure that you may or may not want your child to face.
