29 C.F.R. § 35.13 Exceptions to the rules against age discrimination: reasonable factors other than age.
Title 29 - Labor
A recipient is permitted to take an action otherwise prohibited by §35.10, if that action is based on a factor other than age, even though the action may have a disproportionate effect on persons of different ages. An action is 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.
Title 29: Labor
PART 35—NONDISCRIMINATION ON THE BASIS OF AGE IN PROGRAMS OR ACTIVITIES RECEIVING FEDERAL FINANCIAL ASSISTANCE FROM THE DEPARTMENT OF LABOR
Subpart B—Standards for Determining Age Discrimination
§ 35.13 Exceptions to the rules against age discrimination: reasonable factors other than age.

