The Beast must learn to love and be loved by age 21 to break the curse.
The film establishes this condition in its opening prologue. An enchantress transforms a selfish young prince into the Beast after he refuses her kindness, and she leaves behind an enchanted rose. The spell can be broken only if he learns genuine love before the rose’s final petal falls.
The age is easy to misremember because the film emphasizes the rose’s countdown more than the number itself. The Beast is not required merely to fall in love; he must also receive love in return, making Belle’s feelings crucial to the spell’s reversal.
When Belle declares her love near the story’s climax, the last petal is falling. The Beast transforms back into the prince, and the enchanted castle’s servants regain their human forms. The 21-year deadline is part of this 1991 animated film’s version of the traditional fairy tale.