The age of Mirabel has been confirmed on Twitter by Jared Bush, one of the two directors of Disney's Encanto. The 60th animated feature film from Walt Disney Pictures tells the story of Mirabel (Stephanie Beatriz), the youngest granddaughter of a magical family in Columbia, and the only one to be born without supernatural powers. She is ostracized from the rest of her family due to her ordinariness. But when her family's house, the source of their magic, mysteriously begins to decline in power, Mirabel appears to be the only one who can save the day. However, despite her central role in the narrative, Mirabel's age remains something of a mystery throughout.
As the youngest girl in the family, Mirabel already feels like the odd one out. It only makes matters worse that she has no magical powers, distancing her even more from the rest of her family. Mirabel ends up forming a close emotional bond with her estranged uncle, Bruno, who was ostracized from the family for the opposite reason: his own power of premonition created too much conflict within the family. Despite it all, he never stopped loving his family, and continued living in the Casita with them, hiding in the walls without a single member of the family ever knowing. When Mirabel discovers Bruno in the walls, she helps him to reconcile with the rest of the family, saving the house and its magic through the restoration of love, and proving that she doesn't need powers to be just as important.
Though Mirabel's age is never explicitly mentioned in the film, Encanto co-director Jared Bush confirmed in a series of tweets that Mirabel is fifteen years old. He also revealed the age of the rest of the children in the family. Mirabel is barely younger than Camilo (also fifteen), Isabel is just older than Dolores (both are twenty-one), Luisa is nineteen, and little Antonio is the youngest at five years old.
The implications of Mirabel's age are significant. Bruno disappeared from the family when Mirabel was only five years old. This means that he must have been living inside of the Casita's walls for ten years. It makes his reveal that much more impactful to know that he spent an entire decade remaining faithful to his loved ones, even if they did not welcome him. It's not clear why Bush decided not to make that fact explicit in the film by mentioning Mirabel's age, but the reveal of Bruno is plenty emotional as it is.
It is interesting to see that the people behind Encanto have mapped out aspects of the story that, even if they aren't explicitly stated in the film, act as subtext that helps influence the relationships between Mirabel, her siblings, and her extended family. The writers used these unsaid facts to establish a history for the characters of Encanto. Mirabel's age, even if it isn't explicit, was a serious consideration by the creators during the development process. The emotional moments of the film are infused with the creators' inside knowledge of the characters. Suffice it to say, they did their homework on creating a fictional world that feels lived in.