Iron Man star Robert Downey Jr. has admitted that Marvel could choose to replace him with a younger model down the line, and he seems surprisingly okay with it.
Speaking with Variety, the actor, who has seen something of a resurgence thanks to the popularity of the Iron Man and Avengers franchises in the past decade, was realistic in his expectations for the role, accepting that, at one time or another, it's likely that he'll be replaced by a younger character - as will the rest of the current crop.
The smart money is you have to look at everybody’s age. I’ll put myself at the top of the list. Sooner or later, they’ve got to start over and get somebody young. I’m not there with them yet.
With just two movies left in his current agreement (The Avengers: Age of Ultron and its planned, but as-yet untitled sequel), it's possible that he's trying to push fans to support an extension for his stint as Tony Stark, but it's also likely that, having used the role to propel himself back into the Hollywood A list, he's simply being frank and honest about his future as a comic book action hero.