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 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 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 Mrs. Potts puts Chip into the cupboard, saying "Into the cupboard with your brothers and sisters", between a wideshot and closeup, more teacups suddenly appear around Chip. (00:35:20)
Continuity mistake: When Le Fou and two other men chase the dog-like footrest, Le Fou has a pitchfork and the men have an axe and a sword. However when they bust through the kitchen doors, the sword has turned to a club. (01:13:10)
Continuity mistake: When Le Fou is chasing the dog-like footrest he is missing one shoe, which the dog has, but when Le Fou and the gang burst through the kitchen door, he has the shoe back. Then when the knives scare them away, it's missing again. (01:13:10)
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: The large front doors to the castle open inwards, as seen when Maurice and Belle enter the castle for their first time. However when Belle makes her deal with the Beast, to stay with him forever, the Beast takes Maurice outside, however he opens the doors outwards. (00:13:05 - 00:23:05)
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: When the Beast shows Belle her room, she walks in, and in the wideshot when the Beast says "Now if you need anything...", you can see the whole tiled floor around and under the bed is bare. Then seconds later when Belle runs to her bed crying, and the camera pans out the window, there is a large rug on the previously bare floor. (00:24:40)
Continuity mistake: In the kitchen, the stove says "I work and I slave all day long, and for what?" and the stone wall behind him is bare. Then when it cuts to a close-up of him saying "A culinary masterpiece gone to waste," two shelves have suddenly appeared on the wall behind him, with pots, pans and utensils on them! (00:35:30)
Continuity mistake: When Maurice is getting ready to go back to find Belle, and is pocketing compasses and rolls of paper, he takes a scarf from a drawer, leaving the drawer pulled open, with a red scarf hanging out of it. Then when Gaston and Le Fou enter the house, the drawer is pushed shut with no red scarf hanging out. (00:48:45)
Continuity mistake: When Belle and the Beast eat breakfast, in the scene where the Beast gets covered in porridge, in front of Belle is a decorated glass and a basket of rolls with a napkin over the top. In front of the Beast is just a decorated glass. During shots we see neither one, nor anyone else touch these items. However in the final shot of the whole table, in which Belle and the Beast raise up their bowls, the basket of rolls and the Beasts glass have both disappeared. (00:51:15)
Continuity mistake: When Gaston climbs out of the muddy puddle, he storms off, and it shows Belle's house in a wideshot, with the stone walls surrounding the porch with nothing on them. Then it cuts to a closeup of Belle emerging from the door, but now there's a bucket of seed, and some chickens on the walls. (00:18:30)
Continuity mistake: When Belle's father is in the woods being attacked by bats, when he runs toward screen the bats suddenly disappear. (00:11:40)
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: Whilst Maurice sits in the Masters chair, Cogsworth is knocked down by the trolley with Mrs. Potts on it, and he falls down on the large red part of the carpet. It then cuts to Mrs. Potts, then back to Cogsworth who is still lying down, however now he's suddenly lying on the white part of the rug. (00:15:00)
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.
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.