Georgia has an age discrimination law that appears to mirror the federal law (ages 40-70). It's possible that there are state laws that would go beyond the federal protections and would protect workers at higher ages than 70, and it's possible (depending on his state of residence) that he might be protected by such a law.
As a general matter, however, it ain't prohibited age discrimination if your employer shows you the door after you're 70. It may be cruel and it may be heartless, but it doesn't violate federal law.