employer
(b) The term “employer” means a person engaged in an industry affecting commerce who has twenty or more employees for each working day in each of twenty or more calendar weeks in the current or preceding calendar year: Provided, That prior to June 30, 1968 , employers having fewer than fifty employees shall not be considered employers. The term also means (1) any agent of such a person, and (2) a State or political subdivision of a State and any agency or instrumentality of a State or a political subdivision of a State, and any interstate agency, but such term does not include the United States, or a corporation wholly owned by the Government of the United States.