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: 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: 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.
Other mistake: At no point in this movie is the background of a room ever reflected in a mirror - even if the characters themselves are reflected in it.
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)
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.