You have a point. Hulk has been played by different actors so I don't see why Robert can't be replaced with a younger actor to play Tony Stark. I agree Robert has made this character his own but he is not irreplaceable. James Bond has been played by different actors. Pearce Brosnan was replaced by a younger actor called Daniel Craig because he was getting older. The same thing will probably happen to Robert because he is approaching the big 5. 0. He is not in his prime now. How does he know that no other actor could step into his shoes? What's his problem? He is full of himself. He is not the only talented and charismatic actor on earth. They can find an actor who has as much talent and charisma as him. I can see one actor in the role of Tony Stark: Dominic Cooper. Dominic Cooper came to my mind because he played Tony Stark's father in Captain America, The First Avenger, and I saw lot of Tony Stark in his character. I saw talent and charisma in Dominic as well. I think he looks like the character in the comics. He could easily step into Robert's shoes.
How do you know there isn't any actor out there who has Robert's talent and charisma? How do you know there isn't any actor out there who could do justice to the role of Tony Stark or make the future Iron Man movies successful? Based on what? How would you know if you don't see any new Iron Man movie with a new lead actor?
Don't you think it is time Robert took roles that are of his acting level? He is wasting his talent on these Marvel pop corn flicks.
Are you aware of the fact that you are posting on a Robert Downey Jr fansite??? Do you think any of us will agree with you?