Continuity mistake: When Beast finds Belle in the West Wing room he shouts and she backs up to a nearly destroyed wardrobe, but in the next shot the style of the wardrobe behind her has changed and it's in perfect condition.
Continuity mistake: When Belle opens the door to the kitchen there is no shelf on the wall beside the door, but in following shots one has suddenly appeared with items on it and more things hanging underneath, which changes when Cogsworth lands in the bowl.
Continuity mistake: After leaving the book store, in an overhead shot Belle passes a shop just as a woman is pouring water towards the downspout, and in the next shot the shop suddenly has a large hanging pipe sign and a table under the window, the green shutters have vanished on the right window, the wood trim has changed, etc.
Continuity mistake: When Maurice is tossed out of the tavern we get a nice view of the front with its large hanging sign, but after Gaston whispers his plan to LeFou once again we see the front, which is quite different. The sign is gone, and now there are horns hanging on the awning, etc.
Continuity mistake: When Belle opens the door for Gaston there are six steps to the landing leading upstairs, but when Gaston leaves there are only three steps to the landing.
Continuity mistake: When Belle is reading her book before Gaston walks in to propose, the bellows hangs from a hook on the fireplace stones under the mantle, but when Gaston is talking to Belle the bellows now hangs directly from the wood mantle, though it's back to the original way when Gaston knocks over the rocking chair.
Continuity mistake: When Maurice wakes up and hugs Belle, in this wideshot we see the bag at the foot of the bed and the flap faces Belle, but just before the bag falls over the flap faces the opposite direction, toward the footboard.
Continuity mistake: When Chip fires up Maurice's invention and rides toward the cellar, in the shot facing the cottage we see there's nothing in the cellar handles, but in the closeup as Maurice's machine hacks away at the cellar doors there's a long branch inserted in the handles preventing the doors from opening.
Continuity mistake: After being stabbed with the arrow, Beast falls over a balcony and then falls over on another rounded balcony, next to the edge. Then the angle changes and Beast is lying on the middle of a long rectangular structure.
Continuity mistake: When the Beast shows Belle to her room and then says she will join him for dinner before shutting the door, Belle is wearing her cloak. She's still wearing it when she runs over to the bed, kneels down and starts crying. When we see her again (after the Gaston scene which is in-between), she's no longer wearing the cloak, and she couldn't have removed it at any point because her position next to the bed hasn't changed since she started crying and she doesn't move again until Mrs Potts taps on the door to offer her a cup of tea.
Continuity mistake: When Belle comes down to dinner she leaves her coat in her room. Later, after Belle runs out of the West Wing, she grabs her coat while running down the stairs.
Continuity mistake: When Belle goes to open the door for Gaston, her chair is close to the carpet on the floor. Then when the shot returns to this area, the chair is much further from the carpet.
Continuity mistake: When the Beast shows Belle to her room, in a wideshot you can see the oval centrepiece of the foot of the bed has a large purple rose painted on it and it has a plain red border. In a later scene after Mrs. Potts and Chip leave Belle's room, the purple rose and red border have vanished from the centrepiece, which is now only decorated with evenly spaced gold dots. (00:24:35 - 00:31:05)
Continuity mistake: When Gaston is telling Belle all she has to do is marry him, and her father will be let go from the asylum, his hands are bare. Then when Belle gets the magic mirror and cries "Show me the Beast!", Gaston has yellow gloves on. Then in the next shot they're gone again. (01:07:25)
Continuity mistake: When Belle and the Beast go and sit outside after the ballroom scene, when the Beast asks Belle "Are you happy here with me," between shots Belle's hair goes from being normally hanging down by her back, to resting over her right shoulder. (01:02:45)
Continuity mistake: In the scene where Belle first comes to the gate castle to find her father's hat, she pushes the left side of the gate that's already partly open. But when her father came, he opened the right side of the gate and slammed it shut. How did the left side of the gate open? (00:20:05)
Continuity mistake: When the Beast is getting ready, just before the ballroom scene, the coat stand is cutting the Beast's hair with a pair of scissors that has red handles. Then, in the final shot, the whole pair of scissors is silver. (00:59:40)
Continuity mistake: In the beginning of the movie, Gaston is using a blunderbuss (early rifle) to shoot the birds. He also has a quiver of arrows on his back. But he doesn't have a bow until the end of the movie.
Continuity mistake: When the Beast shows the mirror to Belle she is reflected in it, but for the rest of this scene she isn't.
Continuity mistake: When Gaston says "Now when Belle and I come out that door", you can tell that he has no instrument, only the musicians do. But in the next shot, Gaston has a tuba in his hands, and he slams it on top of Lefou's head.
Answer: In the prologue, it states that the Beast must find true love by his 21st birthday, and that he had been cursed for ten years, so since his relationship with Belle takes place as the deadline approaches, he must have been 10 when he was cursed.