Octorox said:
You must cast based on the scripts written by George Lucas, for example, if you cast an older actor as Anakin he will have to utter the same dialogue that Hayden does and may seem miscast.
Where's the fun in that?
...
Anyways ... I would have casted Keira Knightley as Padmé and Leo DiCaprio as Anakin (or kept Hayden but have someone else do his dialogue).