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).
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.