Q:I am a movie director and I just received the following movie plot. Could you help me answer this question? If not, let me know by writing "Not answerable". Plot title: True Grit Movie plot: Mattie Ross (Hailee Steinfeld), a 14-year-old from Yell County, Arkansas, is determined to avenge the murder of her father. Frank Ross was killed by his hired hand, Tom Chaney (Josh Brolin), after trying to dissuade a drunken Chaney from shooting a fellow card player who had allegedly cheated him. Chaney stole Ross's horse and fled the town. Enraged that no one bothered to pursue or convict Chaney, Mattie decides to take the investigation into her own hands.Leaving her mother and two younger siblings at home, Mattie travels to Fort Smith where her father was killed. She identifies his body for the undertaker. Despite her age, Mattie is extremely quick-witted and confident, and is a fearless bargainer. She sells her father's now useless string of ponies back to the reluctant seller (Dakin Matthews), and acquires three hundred and twenty dollars from the sale. Renting a room at a Fort Smith boarding house, where her father had been staying before his death, Mattie resolves to hire a U.S. marshal to pursue and catch Tom Chaney. After consulting the local sheriff, she settles on the marshal described as the meanest: Rueben "Rooster" Cogburn (Jeff Bridges). After trailing Cogburn to a saloon, she attempts to hire him but is rebuffed. Mattie makes a second attempt after a court hearing at which Cogburn was questioned, but Cogburn turns her down again, doubting that she actually possesses the fifty dollars she offered him as a reward for Chaney's capture.A Texas Ranger, LaBouef (Matt Damon), takes a room at the boarding house and consults Mattie about her endeavor. LaBouef had been tracking Chaney for several months after Chaney had killed a Texas senator in an argument. He offers to combine his knowledge with Cogburn's to track Chaney down. Mattie rejects his offer. The following day, Mattie buys back one of her father's ponies to use on her journey, naming him Little Blackie. She speaks with Cogburn who has decided to accept her offer. However, he initially refuses to let Mattie accompany him as she had planned.... My question: How old was Mattie when her father was murdered?
A:
14 years old