Continuity mistake: When Maurice is being chased by the wolves, he runs up to the gates of the Beast's castle and grabs the bars. You can see in a wideshot that he is holding the bars around the area of the patterned strip of the gate. However when it cuts to a closer view, and he pushes the gates open, he isn't holding the patterned strip of the gate, but just the normal bars. (00:12:35)
Continuity mistake: When Belle talks to the baker during the 'Provincial Life' song, the book in her hand flips between shots - watch the spine of the book - it swaps sides. (00:03:45)
Continuity mistake: When the first song ends, Belle has left the village behind and all the crowd watches her ten meters away. In the close-up and the following scenes with Gaston, she's now very close to the crowd plus a baker with a wheelbarrow has suddenly appeared.
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 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 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: When Belle is walking home with her book and goes up a wheelbarrow, the sacks of flour on the wheelbarrow move closer together between shots.
Continuity mistake: During the song "Gaston", Lefou throws a lot of eggs in the air, but very few come back down.
Continuity mistake: When Gaston and Lefou are talking to the man in the bar, Gaston throws the bag of gold to the lantern's right. However, when this man says, "So you want me to throw her father into the asylum?", the bag is now on the lantern's left.
Continuity mistake: When Lumiere and Belle go into the dining room before the 'Be our Guest' song, in a wide shot when Lumiere says "Ma chere mademoiselle," you can see by the left wall there is a stone statue of a bird. However when it cuts to the following closeup of him, the statue has gone. (00:36:40)
Continuity mistake: In the "Be Our Guest" number, Mrs. Potts notices a large spot of dirt on her side. Then when the napkins wipe her, you can see the one large spot of dirt had turned into three small spots of dirt. (00:39:05)
Continuity mistake: When Gaston comes to Belle's house to propose to her, you can notice that he leaves the door open, but when he backs Belle against it, the door has magically shut. It is definitely the same door - note the items surrounding the door, and the door itself are all the same. (00:17:05 - 00:17:50)
Continuity mistake: When Gastons mob start to bang the front doors with the tree trunk, in one shot of them banging, the door handles are gone. Then two shots later they've returned. (01:10:55)
Continuity mistake: When Belle is coming to the West Wing there is a big statue of a monster with its mouth open very near the door. When Belle is shown running out of the West Wing later, this statue has disappeared.
Continuity mistake: After Belle lets Mrs. Potts in and walks backwards into the wardrobe, the panelled wall is bare. Then in a later wide shot when the wardrobe says "We all think so." there is a wall candelabra in between two panels which then disappears again later, when the wardrobe opens her doors and the moths flutter out. (00:30:20 - 00:31:10)
Continuity mistake: At the end of the film the Beast smashes through the glass window and a lot of it lands on the balcony. When Belle is with the wounded Beast, the glass has vanished.
Continuity mistake: When Belle is in her bedroom at the castle for the first time, Mrs Potts and Chip come in to give Belle a cup of tea. There is tea in Chip when Belle drinks but as the camera closes in on Chip there is no tea. Then as Chip bounces out of the door tea comes spilling out.
Continuity mistake: After the scene where Chip bursts into the cellar, there is a wide shot of outside of the castle as the villagers get beaten up in which the windows next to the doors are gigantic. In other scenes, the windows are nowhere near that big.
Continuity mistake: When Lumiere and Cogsworth are following Belle, they open a door and run into a tower. The shape of the bolt at the bottom of the door changes between shots.
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.