jayembee
Senior HTF Member
When the FF debuted in 1961, the general consensus was that it was 1961 in the comic. Reed and Ben served together in WWII. Ben was a Marine test pilot. I assume he and Reed were mid-20s during the war.
Not only that, but they also knew Nick Fury from the war.
Generally speaking, unless specifically noted otherwise (like war comics, western comics, etc.) comics tended to thought of as contemporaneous. Things eventually got "squishy" mostly due to Marvel wanting to connect their comics to real world events.