What is the movie about an aging female actress?

The movie you are referring to is "Sunset Boulevard". It is a 1950 American film noir drama directed by Billy Wilder and starring Gloria Swanson, William Holden, and Erich von Stroheim. The film tells the story of Norma Desmond, a faded silent film star who lives in a decaying Hollywood mansion with her former husband and butler, Max von Mayerling. When a young screenwriter named Joe Gillis comes to Hollywood, Norma convinces him to help her write a comeback script, and the two begin a relationship. However, Norma's obsession with her past glory and her increasingly erratic behavior eventually lead to tragedy.

"Sunset Boulevard" received critical acclaim upon its release, and it was a commercial success. It was nominated for 11 Academy Awards, including Best Picture, Best Director, and Best Actress (Gloria Swanson), and it won three, for Best Original Screenplay, Best Art Direction, and Best Music Score. The film is considered a classic of American cinema, and it is widely regarded as one of the greatest films ever made.