Kai & aquinas, that has crossed my mind previously as well. Unfortunately, it appears to be the standard, somehow, at most of CTY's peer organizations.
I can understand it to some extent: using age advantages students who have had greater access to advanced content via their grade acceleration. This is why best practice includes provision for calculating individualized achievement scores using grade norms in the case of grade-retained students (so that instructional deficits are not interpreted as individual deficits). One can, however, think of it the other way: using grade disadvantages those who are most likely to need access to services, since they are the ones most likely to have been grade advanced. It seems to me that the solution ought to be to remove caps on the number of students who can qualify, and stick with age. (Since the usual reason for equity-based decision-making is equitable distribution of limited resources.) I can't imagine that the number of US persons who would legitimately qualify for CTY or similar, and who would have an interest in pursuing eligibility, can be so large that they would need to limit eligibility. Limits on accessing courses would occur naturally, in the form of registration maxima, but at least the pool would include a greater number of those eligible.
BTW, SET's eligibility framework is more age-based, with hard cutoffs for age <13.0, and age adjustments for age 13.0-13.7. But that's because everyone is taking the same significantly out-of-level test.
