41 C.F.R. § 101-8.706-2
Reasonable factors other than age
(a) A recipient is permitted to take an action, otherwise prohibited by § 101-8.706-1, which is based on something other than age, even though the action may have a disproportionate effect on persons of different ages.
(b) An action may be based on a factor other than age only if the factor bears a direct and substantial correlation to the normal operation of the program or activity or to the achievement of a statutory objective.