Hmmm.... Do you mean the USAJMO? That's actually linked to the AMC 10, so it shouldn't be restricted to middle school students... the official eligibility rule is:
AMC 10 Eligibility � A student in a program leading to a high school diploma, and under 17.5 years of age on the day of the contest, and not enrolled in grades 11 or 12 or equivalent.
and for the 8 it's:
Any student 14.5 years of age or younger on the day of the contest and not enrolled in grades 9, 10, 11, or 12 or equivalent is eligible to participate.
Those are from the
AMC8 and
AMC10/12 teacher's manuals for this year... Do you have a link that contradicts that? If they're inconsistent I would want a decision from them before we run the AMC10 in a couple weeks!!