The answer to that seems to be some time in your late 30s, if you’re a woman and a Hollywood actor.
 
In this short video from the Inside Amy Schumer video series, Amy pokes fun at the way the entertainment industry treats ‘older’ women. Featuring Tina Fey, Patricia Arquette and Julia Louis-Dreyfus, the women celebrate Julia’s ‘last f***able day’.
 
It is a hilarious take on the ageism and sexism of Hollywood. But if you’re offended by swearing, don’t watch.