But 40-year old actresses get work all the time. Angelina Jolie was never that great of an actress to begin with, and that probably attributes to her lack of work more than anything.
But Amy Adams, Reese Witherspoon, Cate Blanchett, Gwyneth Paltrow, Sandra Bullock, and Octavia Spencer (and there are definitely a bunch more) all continuously find work.
Now what they are paid compared to their Male Co-stars is a different story.