The law applies to employers with 20 or more employees. An employee who is at least 40 years old is in a protected class and can bring an age discrimination claim if an employer took an adverse employment action against that person based on their age. Age discrimination against younger workers in favor of older workers is not illegal. Nor is age discrimination against those who are not forty yet. Example: A clothing store that wants to maintain a youthful image hires college age clerks. As long as the people who were denied jobs because of their age had not reached forty, they would not have a discrimination claim under the ADEA.