Continuity mistake: When the Beast first shows Belle into her room, when he leaves you can see the doors have a curvy, spirally pattern which leads down the them. But when Belle is up in her room crying and Mrs. Potts comes to her door, Belle then approachs the door and we see the design on the door is now two large squares. However in the following shot of Mrs. Potts entering, saying "I thought you might like a spot of tea", the design has changed back to the curvy, spirally pattern. (00:24:45 - 00:30:15)
Continuity mistake: After Beast shows Belle to her room, he slams the door and when Belle leans on the door there are backplates secured to the door, behind the two door handles. However, in the next shot the backplates are gone. (00:24:50)
Continuity mistake: When Gaston spits out the bit of belt during the 'Gaston' song, there is a frog decoration visible. It wasn't there in the opening shot of the tavern though. (00:25:10 - 00:27:20)
Continuity mistake: Right at the beginning of the 'Gaston' song, LeFou sings "no-one slick as Gaston", and we see a man chatting to a lady by the bar, with a barstool right behind him. Then LeFou runs to him and whips off the mans belt, and now the barstool isn't there. (00:26:00)
Continuity mistake: In the tavern, which is the setting for the 'Gaston' song, right at the end of the bar there is a thick wooden beam attached to the bar and the ceiling. You can see this beam clearly when Le Fou sings "No-one's slick as Gaston...", and he prances around and then grabs the beam. However, right at the end of the Gaston song when they sing "So his marriage we soon will be celebrating...", the camera pans backwards out to the window, but the wooden beam has vanished. (00:26:00 - 00:29:45)
Continuity mistake: As Le Fou jumps on peoples heads during the Gaston song, there are three beermugs on the table. However, when he jumps on the table, and is then grabbed by the men, and is being swung back and forth by them, the beers have disappeared from the table. (00:26:20)
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)
Continuity mistake: During the song "Gaston", in the shot where Gaston leaps into the wrestling match, the eagle and warthog head decorations disappear from the wall. (00:28:01)
Continuity mistake: The amount of eggs which land on the floor / on LeFou's face is much lower than the the number which he threw up into the air. (00:28:40)
Continuity mistake: When Maurice is thrown out of the tavern, he falls into a thick pile of snow, near the fountain. However when he cries out "Will no-one help me?", the stone ground outside the tavern is suddenly all snow-free. (00:28:45 - 00:30:00)
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: When Belle meets Mrs Potts for the first time, Belle approaches the door to let her in. In the shot of Belle walking toward the door, the door handles are both the vertical "thumb-button" latch that you would grip the handle and push down on the thumb piece (with your thumb, of course) to release the latch. But in the next shot when she opens the door (and when she is first shown her room), the door handles are diagonal "lever style" handles that you have to turn downward with your whole hand to open the door. (00:30:10)
Continuity mistake: When Belle opens the bedroom door for Mrs. Potts and Chip, in the close-up the bottom corners of the doors are aligned perfectly with the edge of the floor tiles, when both doors are closed. Later, when Cogsworth comes in to announce dinner, the bottom corners of the doors are above the center of the tile, when the doors are closed. This should never change. (00:30:15 - 00:31:20)
Continuity mistake: When Belle lets Mrs. Potts in, she then walks backwards into the wardrobe, and you can clearly see the wall from the bed to the corner is made up of three large purple wall panels. However in a later shot, when the wardrobe opens her doors and the moths flutter out, the wall is now made up of four purple panels. The design on the panels differs too. (00:30:20 - 00:31:10)
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: When Mrs. Potts and Chip go to Belle's bedroom, the small colorful decorative pillows that lie on Belle's bed disappear, then reappear, etc., and the three large pillows change their appearance and position in the following shots as well. (00:30:20 - 00:31:05)
Continuity mistake: When Mrs. Potts, Chip and the milk and sugar pot enter Belle's bedroom, they make some tea in Chip, who then hops over to Belle. After they pour and make the tea in Chip, as he hops off, in a closeup you can see the milk pot is standing beside Mrs. Potts and the sugar pot is next to the milk pot. Then when it cuts to a wider view, the milk and sugar pot have swapped places with each other. (00:30:30)
Continuity mistake: When Cogsworth comes into the study to say that Belle isn't coming for dinner, he opens the door inward and doesn't shut it. In the next shot of the doors from the hallway, though, the doors are closed, and the Beast opens both doors outward. They aren't double-swing doors like the kitchen ones. (00:32:30)
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)
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.