If he takes algebra when he is 10, then geometry when he is 11, it is very possible that he will score 700+ prior to the age of 13 without studying.
As others have mentioned, the math on the SAT is not hard. Getting 700+ is mainly a matter of not making silly mistakes. My eldest is not a math type. She didn't do that well on the SAT math when she took it in 7th grade, but she got a 730 when she took it in 11th (that was two wrong, skipped one question - there are a total of 54 questions on SAT math).
My middle kid took the SAT in 7th when she was halfway through Algebra I. She is clearly better at math than my eldest. She did one 25 minute practice section of math prior to the test - she got a 580. This year she is in 9th and she took the PSAT (because the school makes all 9th-11th graders take it). She refused to open the practice booklet, but she managed a 71 (equivalent to a 710) on the math.
I wouldn't worry too much about prepping him for the test. Perhaps he should do a practice test under timed conditions just to get an idea of the length of the test - my kids felt the SAT was largely a test of endurance. I can also see that scoring well on the SAT and ACT has something to do with speed, as others have mentioned. My older two kids are no where near PG types, but I recall that they had high PSI on the WISC - they can really motor through tests like SAT/ACT.
