Felicity has a heck of a resume, including Star Wars: Rogue One, the indie darling Like Crazy, and The Theory of Everything, for which she earned an Oscar nom. She's been acting since 1996, though! Here she is in her second credited role, in The Worst Witch when she was 14–15 years old:
Sophie Marceau - 14 years old in "la boum"
and
Natalie Portman - 12 years old in Léon