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Typically, tests are scored by age, so his youth should have been accounted for in the percentiles. However, one of the unusual attributes of SAGES-2 is that it has both general norms and gifted norms. Find out whether his percentiles were based on the gifted or general population norms. That could make a big difference, as even 70th %ile on gifted norms would be quite strong.

...pronounced like the long vowel and first letter of the alphabet...