premise: How to prove age discrimination in hiring<br>Read up on federal law. Federal law prohibits discrimination in hiring on the basis of age when the applicant is 40 or older. The primary motive for refusing to hire someone must have been age.
hypothesis: Employers in the past have considered 40-year-olds too old to hire.
reason: This has to be true for some employers, otherwise why would there be a federal law prohibiting the discrimination of those age 40 and above?