No, a help-wanted ad that seeks “recent college graduates" may discourage people over 40 from applying and may violate the law. The Age Discrimination in Employment Act (ADEA) forbids age discrimination. It is illegal, under federal law, for an employer to publish a job advertisement that shows a preference (or discourages someone from applying for a job) based on race, color, religion, sex (including pregnancy), national origin, age (40 or older), disability or genetic information.

Source:Prohibited Employment Policies/Practices, http://www.eeoc.gov/.