As far as their ages, it's different in the original book... but then we're not talking about the novel here, either! And yes, I would say they're around 4 to 5 years apart, as jordangirl says, because Elphaba remembers the birth.
In the book, Glinda and Elphaba would be the same age, though. Nessa doesn't start at Shiz until later on. Of course at the end of the book, when Elphaba "dies," she's also 38 years old. (The same age as Margaret Hamilton when she played the Wicked Witch in the MGM movie). That was Maguire's intention.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22