Shakespeare clearly states that Juliet is 13 years old (while leaving us to guess about the age of Romeo). He less clearly states that Hamlet is 30, although he could also be 16. I'm sure there are other examples, but those are the ones that come readily to mind.
So, here's the game. Pick a character, ideally one whose age is not spelled out in the text :), and then pick *2* different ages for that character, and tell how the story might play out differently.
This idea came up over in the Othello's Ancient thread regarding Iago's age. On the one hand Iago could be a seasoned old soldier, roughly the same age/experience as Othello, who would make a fairly obvious case for Iago being a jealous rival of Othello's success. *OR* Iago could be a much younger, minor officer - someone who Othello barely gives the time of day to. That is, until Iago has the chance to say "Welll, I didn't want to say anything, buttttt....." and Othello suddenly cozies up to Iago as his new best friend, the new best friend that is that will spy on Desdemona for him. This would explain why Iago so easily blindsides Othello, since he's hardly on Othello's radar until it all goes down on stage.
Got the idea? Ok, who's got one? We do NOT have to dig in and say "Well, yeah, no, according to historical fact that would never have happened...." It's just supposed to be fun. Pretend you're the director and for a given actor you've got to decide between casting someone of age X or age Y. Which do you pick, and how does that alter the vision?