In the upcoming movie [X-Men: Days Of Future Past](movie:203942), Quicksilver is making his first appearance into the Marvel Movies. Evan Peters has taken on the role and is going to be apart of the X-Men Movies,but Aaron Taylor-Johnson has also taken the role in [The Avengers: Age Of Ultron](movie:293035) aka Avengers 2. Obviously there is a major age difference. Quicksilver (X-Men DOFP) is probably around 19 maybe even 20. Evan Peters is actually 27, but he is playing a younger role. On the other hand, Aaron Taylor-Johnson looks like he is playing someone in their 30's, but Aaron Taylor-Johnson is 4 years younger than Evan Peters (23 years old).
You guys are probably wondering, what does this have to with bringing the X-Men and the Avengers together? Well, Disney owns the rights to the Avengers and FOX owns the rights to X-Men so that means that Marvel has two options. They can either somehow incorporate Disney and Fox into one contract to make a giant X-Men and Avengers team up or maybe X-Men Vs. Avengers, but which side would Quicksilver and Scarlet Witch would be on? Unfortunately, the X-Men and Avengers movie has a less than one percent chance of happening.
The other option is that one of them change the origin stories and the official term for them (Mutants, Half-Gods etc.) and then there won't be anyone suing anyone else.