[throwaway2037]

I assume you are referring to United States employment law?

For others: https://www.eeoc.gov/age-discrimination

U.S. Equal Employment Opportunity Commission

Age Discrimination: <<The Age Discrimination in Employment Act (ADEA) forbids age discrimination against people who are age 40 or older. It does not protect workers under the age of 40, although some states have laws that protect younger workers from age discrimination.>>

[mattkrause]

Yes, but it's similar in Canada and Germany* too.

* German academia has some incredibly stupid rules related to time-since-graduation, but age per se is a protected class.