Continuity mistake: When Lizzie was performing at the music awards, you can see some people walking near the stage (on stage left) but in the next shot, those people are gone.
Factual error: When Lizzie was performing, there's no stairs in the shots of the crowd.
Continuity mistake: If you pay close attention, Paolo's accent doesn't always stay the same. At most times, there is a clear Italian accent, but at others, an American accent can be heard.
Continuity mistake: In the sceen where Kate first appears in the airport and says "How many Lizzies does it take to screw in a lightbulb..." there is a parked airplane visible in the window behind her. After a quick cut to Lizzie the scene cuts immediately back to Kate and the airplane is gone. Airplanes don't leave the gate that quickly.
Visible crew/equipment: When Lizzie and Paolo run up to where they watch the fireworks, their tape marks are visible on the ground.
Visible crew/equipment: When Lizzie and Paolo are walking around on their date (After Paolo gives Lizzie the flower), you can see the boom mic in the top of the screen (on VHS).
Revealing mistake: In the scene where Paolo and Lizzie are at the designer's studio, and Lizzie is talking to Paolo while wearing the green outfit, you can see the cord at the back of her neck that made the skirt pop up when she pulled the dangley things in front of her face. (00:43:45)
Factual error: In the scene where Paolo first meets Lizzie at the Trevi fountain, wouldn't he be swarmed by an army of photographers or at least a bodyguard or two? A popstar as famous as him probably couldn't go out alone in public like that.
Continuity mistake: In the scene where Lizzie is talking to Paolo in the restuarant, Lizzie says something like, "and what about you". Then Paolo says "for me it's no problem"; but when he says this his Italian accent is gone. (00:31:39)
Audio problem: At the end of the movie when Lizzie is singing, her lips don't sync with the music.
Continuity mistake: In the scene on the Vespa on Lizzie's second day of sneaking out she is wearing a pink collared shirt but in the exact next scene she is wearing an orange shirt and a jacket.
Other mistake: At the graduation, when the girl says to Kate, "It's like watching those poor animals on the discovery channel," you can see Kate mouthing her lines.
Continuity mistake: When Lizzie's parents go to the hotel in Rome to find Lizzie, Lizzie's mom puts her hand on her husband's shoulder at one point. The shot cuts and her hand is down, the shot cuts again and it's on his shoulder again.
Continuity mistake: When they arrive at the hotel, Ms Ungermeyer (Alex Borstein) says, "Welcome to hotel & 8230." During this time, she has a clipboard lying on her left forearm. Cut to a different angle (her back facing the camera) as she walks now she is just holding the clipboard with her left hand. Cut back to the previous angle and the clipboard is resting on her forearm yet again.
Continuity mistake: When there are back shots of Lizzie facing the audience when performing the part "Dreams!" You can see that the single audience members are way smaller than her and go beneath her waist. But in other close shots of the audience, they are near her and very close to size.
Continuity mistake: In the begining of the movie when Lizzie is trying to pick out an outfit for graduation, she rummages through her closet twice. The second time, you see her in a shot from inside the closet. Lizzie is wearing the outfit with the blue shirt that she changed into to sing the song. The next shot is of Lizzie from outside the closet, with her other outfit on-the one she was wearing when her brother drove his camera into her room. In the next shot from inside the closet again, she is wearing the outfit with the blue shirt on again.
Answer: In the TV show, they are 13-14 years old. Assuming this is after the TV show, and we never see Lizzie, Gordo or Miranda celebrating their 14th birthdays (we see Kate celebrating her '14th' birthday and Gordo celebrating his Bar Mitzfah a year late), Lizzie and Miranda are 13-14, Gordo is 14 and Kate is 15 (it is mentioned in an earlier episode that she was held back a year in Kindergarten.) This is only an assumption, due to the TV show.