Anyway, one thing about the latest trilogy of x-films is that that are firmly rooted in specific eras of recent history (the 60s, the 70s, and the 80s), even if their evocation of those eras is more akin to Happy Days than Mad Men in accuracy. This is a departure from the Marvel Studios films which are always up to the minute "now" (except flashbacks) and most comic books which are in a strange present, that keeps getting retconned as time moves forward. Stan and Jack may have told us that Reed and Ben fought in World War II but by Byrne's Lost Generation limited in the '90s, they weren't even out of college in the 80s--and now they are probably younger than me.
The reasons for this are understandable, but it doesn't have to be that--in the comics or in your superhero rpg campaign. Maybe most campaigns don't run long enough to see much history pass during them even if you had the sessions take place more or less when they were played, but there's no reason you can't start in the past and skip ahead, playing a certain number of sessions in each era or maybe establishing a "legacy setting" by running a short campaign as "the Justice Society" before moving to the present (or at least a couple of decades) to play their legacies. The setting quickly gets historical depth that means more to the players than backstory the GM just made up.