Sophie Turner was only 13 years old when she was cast in Game of Thrones, but with the HBO show heading into its eighth and final season, it's easy to forget how old Sophie is exactly. So, how old is she, you ask? Well, Sophie was born on Feb. 21, 1996, making her 21 years old. She's already celebrated her birthday this year, but she's got another reason to celebrate seeing as she just got engaged to her 28-year-old boyfriend, Joe Jonas. Wow, 2017 is turning out to be a great year for Sophie.