Major U.S. employers use social media’s ability to display job ads only to those in certain age groups, such as between age 25 to 36, or below age 38 or below age 50. They are using this feature to advertise job openings only to younger workers, thereby removing older workers from their candidate pool.
Examples:

• Verizon targeted showed ads only to those age 25 to 36 years old
• UPS targeted age 19 to 35
• State Farm targeted age 19 to 35

Reporters found they could readily purchase job ads based on age profiles at Google and LinkedIn.
Health care employers ran ads based on sex, targeting female nurses (nursing is 90% female) and using ad tactics that may avoid reaching men. Employers can also use social media targeted advertising to intentionally reach – or discriminate against – ethnic and minority groups.
Facebook says age-based job ads are justified and does not plan to stop the practice by employers. Critics point out that as job seekers discover Facebook promotes age discrimination in job advertising, job seekers will go elsewhere.
A class action lawsuit has been filed against Facebook on behalf of all Facebook users 40 or older.
Personal Note
I do not believe I have ever seen a job ad on Facebook.
I have a undergrad degree in computer science, a graduate degree in software engineering, and an M.B.A. degree, and have worked in Silicon Valley and for Microsoft Corporation.
I am skilled in the top 3 most sought after fields in the United States. But I have never seen a job ad for my field on Facebook. Ever. I am also over 50 years old.