Jennifer Aniston Fabulous at 40!

By Michelle Tauber

UPDATED 02/23/2009 at 01:00 AM EST • Originally published 02/23/2009 at 01:00 AM EST

Wrinkles? Nope. Flab? Hardly. Gray hair? Yes! Well, one, anyway. In what may be the only outward sign that Jennifer Aniston is, in fact, getting older, she told Ellen DeGeneres on Feb. 5 that the sight of a "really long gray hair ... kind of flipped me out." Not that anything could stop her from celebrating. Four days before her 40th birthday on Feb. 11, the actress hosted a lavish bash for more than 50 guests at her newly renovated Beverly Hills home, where friends such as David and Courteney Cox Arquette Arquette, Sheryl Crow and Diane Keaton celebrated and dined on food from famed deli Nate 'n Al. "I told her she's got a lot to look forward to," says Crow, 47. "Jen is just beautiful, inside and out."

Also on hand—with a song he wrote just for the occasion—was Aniston's boyfriend, John Mayer, 31, who told DeGeneres that he and Aniston have "sleepovers" at her high-tech new home. Her career is hot too: She's kicking off her new decade with a No. 1 film, He's Just Not That Into You, and just signed on to another romantic comedy, The Baster, with Jason Bateman. So what's a gray hair now and then? As a content Aniston told DeGeneres, "I feel better than I ever felt in my life."