Well, think about the episodes when they go to school. The school is called "Peach Creek High School" so, maybe around 14, 15, o 16. With the exception of Sarah and Jimmy, who are about seven. I remember that being mentioned in an episode.
jimmy and sarah are probably,like 10 o 11....and everyone else is twelve(i know for a fact a card in eddy's wallet sed he's 12) and they're all in jr. high (middle school)