While many fans hoped to see Iron Man and War Machine team up again in Iron Man 3, they got the stripped down version with Tony Stark and James Rhodes fighting side-by-side instead. Then Stark couldn't even give Rhodey one of his suits so they could team up and fight Extremis soldiers together (boo). So Rhodey went and saved the President and took off with him and his rebranded Iron Patriot suit. 'The End' for the Iron Man and War Machine team up, in Iron Man 3.
So what's the point of bringing all of this up? The point is that in an interview with USA Today—without quoting the actor via Screen Rant—actor Don Cheadle said he "has a part" in Avengers: Age of Ultron. Maybe, just maybe, we will get to see War Machine (or Iron Patriot) kick some butt again.
No further details were provided by the actor, therefore fans can only hope Cheadle is referring to the possibility to kick some Ultron butt with Iron Man and both men suited up. Or, and speculated as being most likely, fans will see Rhodey in a quick scene and it'll just be a cameo. One can only hope for the former.
Until Marvel Studios or Avengers: Age of Ultron writer/director Joss Whedon confirms any of this we can only speculate as how much (or little) Rhodey will be in the film and/or if he'll even be in his own armor. And, by the way, there's been lots of fan chatter asking Marvel Studios to bring back War Machine armor over seeing the Iron Patriot suit again.