Continuity mistake: In the 'Gaston' song sequence, near the end, Gaston is sitting in his huge antler chair with Lefou. In the wide shot, there is a bear rug behind the chair. The camera does a close up of Gaston, then in the next wide shot, the chair is on top of the bear rug. Also, after this, Gaston gets up off of the chair and in the next shot, both the chair and the rug disappear completely. (00:29:20)
Continuity mistake: Belle opens the door outward so Gaston falls out, but after she throws his shoes at him, she slams it shut from the inside. (00:18:00)
Continuity mistake: When Belle is taking her book back in a basket at the start of the film, its colour changes from red to blue, back to red, then purple in the book shop owner's hand, then finally red on the shelf. (00:03:00)
Continuity mistake: When Gaston comes in to propose to Belle, his boots are clean until he puts them up on the table, then suddenly they're covered with mud. (00:17:25)
Continuity mistake: In the scene after the wolf attack, Belle is trying to put a cloth to the Beast's wounds, and they then shout at each other. When the Beast yells "Well you shouldn't have been in the West Wing," you can see that he has three slashes on his arm. Then when Belle puts the cloth on the wounds, there are suddenly four slashes. (00:47:15)
Continuity mistake: When Gaston comes in to propose to Belle, he sits in the chair and kicks of his boots etc., and between shots there's a bellows hanging by the fireplace which keeps disappearing and reappearing. (00:17:30)
Continuity mistake: At the end of the song "Belle", there's an overhead shot in which you can tell that there is no mud on the street in front of Belle. Then a few seconds later, there is a big puddle of mud, and Gaston throws her book into it.
Continuity mistake: When Gaston has his feet on the table, the amount of mud on the book and tablecloth changes between shots.
Continuity mistake: At the end of the movie, Belle shows the Mirror to Gaston and the other people in the village. She's wearing a white apron over her blue dress. When Gaston takes the mirror from her, the apron is gone. A few seconds later, it's back. (01:06:35 - 01:07:20)
Continuity mistake: After the wolf attack, it fades to a shot of Belle who is pouring hot water out of Mrs. Potts, into a bowl. In this shot Belle is kneeling on the large white decorative design embroidered on the large red rug, and the little bowl also sits on the design too. Then when it cuts, Belle is suddenly kneeling on the red part of the rug and the bowl sits on the red part too, and the Beasts chair is now sitting atop the large white design. (00:46:50)
Continuity mistake: In the scene where Gaston proposes to Belle, Belle crosses in front of a mirror, and she has no reflection. A second later, Gaston crosses in front of it, and he does have a reflection. (00:17:05)
Audio problem: When Mrs. Potts is talking to Belle for the first time, in her bedroom, Mrs. Potts says "It'll turn out alright in the end. You'll see." However, when she says "...you'll see" her mouth remains closed. (00:30:50)
Continuity mistake: In the newer version of the film, there has been a new song called "Human Again" added. When standing at the foot of the stairs, Cogsworth replaces a cog in himself, opening his door, with the hinges on his right. All the other times he opens it though, the hinges are on the left. (00:54:35)
Continuity mistake: When Gastons mob throw Belle and Maurice into the cellar, Belle then tries to wedge open the window with a long wooden pole. She fails, then turns to Maurice, leaving the pole sticking out and laying on the windowsill. Then when the shot changes and the camera pans to Chip looking through the window, the wooden pole has gone. (01:09:40)
Continuity mistake: When Belle won't come out for dinner, the Beast storms off, slamming the door, so that bits of plaster fall from the roof, onto Lumiere, all over the floor. However in the final overhead shot of this scene, the plaster has vanished from the floor. (00:33:55)
Continuity mistake: In the scene after Gaston proposes to Belle, Belle walks out of the door and then to the barn. As she passes the cellar doors, saying "...Me. The wife of that borish, brainless...", you can see that there is a small window either side of the cellar doors. However, later on into the film, when Maurice and Belle are trapped in the cellar, Chip gets Maurices invention to work. Then, as the machine hurtles towards the cellar doors, the small window on the left side of the cellar doors has vanished! (00:18:40 - 01:12:05)
Continuity mistake: When Belle climbs the ladder in the bookshop, at the top of the ladder there is a very large space with no rung in it. Seconds later, when Belle slides the ladder across, a rung has appeared in the space. (00:04:25)
Continuity mistake: When Belle is trying to get up the stairs to the West Wing, and Cogsworth and Lumiere are trying to stop her, when Belle says "You have a library", you can see that Belle is standing six steps up from the foot of the stairs, and that Lumiere and Cogsworth are standing on the seventh step up from the foot. However when it then cuts, and they all start to climb back down the stairs, Belle is now on the third step up from the foot and Cogsworth and Lumiere are on the fourth. (00:42:05)
Continuity mistake: When Gaston proposes marriage to Belle, there is a thick pink cushion on his chair. But when Gaston sits on it and puts his feet on the table, the cushion is much thinner, and it is now red.
Continuity mistake: During the 'Gaston' song in the tavern, Gaston spits out a bit of belt which knocks a pot onto Le Fou's head, which gets stuck. When the pot strikes him and he falls to the floor, you can see there is no metal pole running across the bottom of the bar. In every other shot of the bar, there is a metal pole which runs across the bottom of it. (00:27:25)
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.