Continuity mistake: When Belle is reading her book by the table, a shelf over the fireplace is visible below another shelf to the left of it. Moments later, after Gaston has entered and Belle asks "What do you know about my dreams?" this shelf is above the shelf to the left of it.
Continuity mistake: Near the end, as the objects arrive and are watching as Belle helps Beast lie down, the rose stem is shaped as a question mark. A few seconds later, viewed from the same direction, when the last petal falls the rose stem is now shaped as a reversed question mark. (01:14:40)
Continuity mistake: After Belle sees the painting in the West Wing, there is a shot of the table where the enchanted rose is. In this shot, the magic mirror is not on the table. In the next shot, it is. Then when the Beast yells "Get out." it is gone again.
Continuity mistake: In the newer version of the film, there has been a new song called "Human Again" added. When the little dog-like footrest runs across the hallway, chasing the cat-like cushion, he leaves black footprints all over the floor, and then he skids to a halt, leaving circular swerve marks over part of the floor. However when it cuts to an overhead shot, the line of footprints along the floor runs much shorter and there are now more sets of swerve marks. (00:57:25)
Continuity mistake: During the film's introduction, as the camera pans away from the castle during the storm, there is a crack of thunder and a lightning flash. As the lightning strikes you can see a black branch growing on the side of the castle/cliff disappears after the flash of lighting. The animators forgot to draw it, so it just vanishes. (00:02:25)
Continuity mistake: When Belle finds Maurice locked in the dungeons, the bars change from black to brown in different shots.
Continuity mistake: When Belle comes to the West Wing, she approaches a cracked up mirror. Then in the shot where she is shown right in front of the mirror, the crack on the top right is much wider, and many cracks are differed etc.
Continuity mistake: When Mrs. Potts and Chip first come into Belle's room at the castle, Chip spills tea onto the carpet. In the next shot, the tea is gone.
Continuity mistake: When Belle talks to her father through the bars, when he is held prisoner, between the first two shots, Maurices arm changes from sticking out of the middle bars to out of the side bars. (00:21:35)
Continuity mistake: As Belle is walking through the bustling market whilst reading her book, and Gaston is following her, and we hear the lines "Good Day" "Bonjour" "You call this bacon" "What lovely grapes", Belle has no basket hanging from either arm, clearly visible in a behind shot of her walking. It then returns in the beautiful closeup, when the camera pans around with her and she sings, with outstreched arms, "There must be more than this provincial life." (00:07:30)
Continuity mistake: At the start, the Beast tears a painting and makes ten equal sized gashes. Later, Belle is exploring and sees this painting; there are now nine little gashes and one huge gash.
Continuity mistake: When Belle enters the bookstore, the windowsill is red. When she comes out of it, it is white.
Continuity mistake: Gaston's socks are red when he is in the mud. When he walks away, we briefly see them as being orange.
Continuity mistake: At the end of the 'Something There' song, Belle is sitting at the fireplace and Beast hangs her coat up on a stand. Next to the coatstand you can see a bookcase with a statue on top of it. However when it suddenly cuts to Cogworth and Mrs. Potts, who are watching them from the doorway, still singing, the coatstand, bookcase and statue have all vanished. (00:53:25)
Continuity mistake: When Maurice arrives at the castle and loses his hat, the bricks the hat is over change between shots.
Continuity mistake: In the slightly changed version with the song 'Human Again' added, when Cogworth, Mrs. Potts, Chip etc. are talking about there being "Something there that wasn't there before...", just after the "Something There" song, In this scene Chip's chip is in the left side of his cup. It is meant to be in the right. (00:53:35)
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 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.
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.