Cameron Diaz, Gwyneth Paltrow, Ben Affleck and more! See the seemingly ageless A-listers celebrating 40th birthdays this year
Eminem (October 17)
The "Lose Yourself" rapper says he's mellowed as he's gotten older -- and that his art has matured right along with him. "Anything I've ever said, I certainly was feeling at the time," he told the New York Times in 2010, addressing his often controversial past hits. "But I think I've calmed down a bit. My overall look on things is a lot more mature than it used to be."