40 CFR 7.155: Exceptions to the rules against age discrimination—reasonable factors other than age.

A recipient is permitted to take an action otherwise prohibited by §§ 7.140 and 7.145 which is based on a factor other than age, even though that action may have a disproportionate effect on persons of different ages. An action may be based on a factor other than age only if the factor bears a direct and substantial relationship to the normal operation of the program or activity or to the achievement of a statutory objective.