The organization, originally founded for retired people, is honoring PEOPLE's twice-named Sexiest Man Alive (1995 and 2000) with a special edition birthday cover of AARP The Magazine.
"Acclaimed Actor, Producer, Humanitarian, and Family Man, Mr. Pitt Joins the Club" reads a line on the mock cover.
In an interview with PEOPLE last December, the father of six talked about turning the big 5-0 and being conscious of getting older.
"I want to make sure I'm doing things of value – that mean something to me," he said. "Make sure I'm doing things I've always wanted to try. And make sure I'm not doing things I don't want to do. Because I'm very conscious of time; I know it's limited."
One person he won't be asking for advice – his pal George Clooney, who is 52.
"He's too old. We live different lives," Pitt laughed. "What can he tell me? Other than how to protect my liver!"