Isn't it somewhere in the neighborhood of 15-20 years have passed in the Marvel Universe since the "beginning" with the Fantastic Four's accident?
I go with 15+. In The Thing
#8 by Dan Slott, Ben had a Bar Mitzvah ceremony marking 13 years since he was "reborn" as The Thing. That was just before Civil War
. Since then, Captain America was "dead" for about a year of story time (as per Captain America
600, which led into "Reborn"), and we can assume that a year of "Marvel time" has passed since Cap's return.