Continuity mistake: During "Gaston", Gaston shoots his blunderbuss three times. However, four holes appear in the ale barrel.
Continuity mistake: After the brawl between the villagers and the objects, a lot of mess is on the floor. Then when the objects jump for joy, the mess is gone.
Continuity mistake: In the shot of Belle reading her book in her house, the spout of the black kettle on one of the shelves is not visible. In the following scene, when Gaston is talking to Belle with his feet on the table, the spout is visible.
Continuity mistake: When Gaston is cleaning his teeth in front of the mirror, the decorations on the mirror's frame change between shots.
Continuity mistake: When Maurice looks into the castle after arriving, there are no yellow edges around the red carpet. Yet moments later, they appear.
Continuity mistake: When the Beast claws the painting of himself in human form, he tears his right eye. When Belle comes into the West Wing later, neither of his eyes are torn.
Continuity mistake: Just before the new "Human Again" song, Cogsworth is telling the other servants what to do. He is standing on the dog/footstool and tells everyone to clean up the castle. All the servants run off including the dog/footstool and Cogsworth falls down the stairs. A load of cogs fall out of him and Lumiere picks one up. It is quite small but as he dusts it off it grows and when he hands it to Cogsworth and it has grown in size again to over double the size it was when it first fell out of him.
Continuity mistake: In the Gaston song sequence, the villagers pick up the chair Gaston is in, and carry it in front of the bear rug. Then suddenly, Lefou is standing on the bear rug, and the chair crashes down on him.
Continuity mistake: When Belle approaches the West Wing, she sees a door and there is one statue holding candles next to it. However, when Belle runs out, there are statues on both sides.
Continuity mistake: When Lumiere and Cogsworth are persuading Belle not to go into the West Wing, in an overhead shot they're at the center of the red carpet, but in the next they're at the far edge of the carpet.
Continuity mistake: When Gaston is singing "Kill the Beast", he is scaring Lefou. Lefou has a bit of his white shirt visible underneath his coat. When he is climbing backwards up the stairs, this spot has changed to green. When he marches away, the spot is white again.
Continuity mistake: When the villagers burst into the castle using the tree trunk, they put it down in front of the door, but later it's gone.
Continuity mistake: When Maurice is gathering his belongings and says, "Somehow I'll get her out of there.", to the side of the door there is an umbrella and a coat hanging slightly to the right of it. However, when Gaston bursts in, shouting, "Belle? Maurice?" the coat is now hanging directly over the umbrella.
Continuity mistake: Adding to the mistake about the bear rug moving around, it also changes physical form. Sometimes it is a light brown, fat and un-realistic looking. Other times it can be seen as a dark brown/black flat bear which looks very real. This change occurs many times during the scene.
Continuity mistake: When Belle uses Maurice's invention to look outside the door, there is a wooden bolt on the wall. The length of this bolt changes between shots.
Continuity mistake: When the villagers are marching to the castle, in a wide shot Gaston holds the mirror with his left hand, but in the next shot as he yells "We will siege to the castle" it's in his right hand.
Continuity mistake: When Maurice is taking his invention to the fair, there is a covering over the machine with a brown patch on it. But in the shot where Maurice says "It's a shortcut, Phillipe", the patch is now white. Also, when Phillipe comes back to the house later, and Belle takes the machine off him, the patch has disappeared.
Continuity mistake: When Maurice lets Lumiere fall to the floor, the cracks Lumiere is over change between shots.
Continuity mistake: In the newer version on VHS by Disney, including the song 'Human Again', that added scene completely messes with the movie. During the scene the servants clean up the castle and make it pretty and happy. However, when it switches back to the scenes from the original movie, the outside of the castle is no longer clean until the end of the movie and the spell is broken.
Continuity mistake: When Lefou is jumping on peoples' heads singing "You can ask any Tom, Dick or Stanley" the position of the beer mugs on the table change between shots.
Answer: The Rose started wilting at The Beast's 21st birthday and could have presumably started wilting years before the first time we saw a petal fall off. Given the fact that Lumiere stated that they were living with the curse for 10 years, prince Adam could be 23-24 years old at the time of the original movie,13-14 at the time of the curse, and the Rose could have been wilting for two to three years. This is my best guess given the approximate age of Prince Adam in the ripped up portrait before he was the Beast.