According to ethe Civil War files that "Tony Stark" writes for the president, only about 15 years has passed since the Fantastic Four got their super powers. Which I guess would make some sense, I mean Spider-man started being Spider-man when he was about 15, he's about 30 now? Something like that. So yeah, only about 15 years has passed in the Marvel Universe. Tony writes, "Over ten years ago, when Reed Richards' unauthorized space flight returned to Earth, ushering in a new age of super heroes, the Fantastic Four were quarantined by the U.S. Air Force." So yeah... there you go.