^But the sliding timeline approach, moving events from the past closer to the present, means that Magneto would've been an old man by the time he first met Charles Xavier.
An idea I've thought of is that instead of moving past events closer to the present, current events can be shifted into the past. Say, for the sake of the argument, the Age of Marvels began on Earth-616 in the year 1983; the general idea is that as of stories published in 2010, around 13 years have passed since FF#1, so stories published within the last year actually happen around 1996 on Earth-616. I don't think the length of time from FF#1 can be more than 15 years, personally.
An idea I've thought of is that instead of moving past events closer to the present, current events can be shifted into the past. Say, for the sake of the argument, the Age of Marvels began on Earth-616 in the year 1983; the general idea is that as of stories published in 2010, around 13 years have passed since FF#1, so stories published within the last year actually happen around 1996 on Earth-616. I don't think the length of time from FF#1 can be more than 15 years, personally.