It's been confirmed Scarlet Witch will appear in THE AVENGERS: AGE OF ULTRON, however Elizabeth Olsen starring as the character has just been a rumor so far. Granted it does sound like a very likely rumor, but there hasn't been an announcement from Marvel saying Olsen is definitely playing the character.
It might not be an official press release from the studio, but Samuel L. Jackson has confirmed Elizabeth Olsen will play Scarlet Witch in THE AVENGERS: AGE OF ULTRON while talking to The Wall Street Journal. The actor also said filming for the movie with director Joss Whedon won't start until after March of next year.
“I don’t think we begin shooting before March of next year,” Jackson said of “The Avengers: Age of Ultron,” the next film to begin shooting in the Marvel universe. ”I know we’re shooting in London, that James Spader is Ultron and going to be the bad guy, and that we added Ms. [Elizabeth] Olsen [who will play the Scarlet Witch], but I don’t know what she’s doing, if she’s on the inside or the outside. I haven’t seen a script.”
When the rumor was first announced, some of you weren't too pleased with the idea of Elizabeth Olsen as Scarlet Witch. I for one think she could do a great job, but it's also going to depend on how the character is used. Joss Whedon previously said Scarlet Witch and her brother Quicksilver interested him because they "represent the part of the world that wouldn’t necessarily agree with The Avengers," so maybe they'll start as villains or at least a pain in The Avengers' ass before switching sides. Just speculating, but it will be interesting to see how Whedon uses these new characters in the upcoming film.
THE AVENGERS: AGE OF ULTRON will be in theaters on May 1st, 2015.