Writers generally had little to say about the life of Steve Rogers before he became Captain America. In the late seventies the writers of the book decided that perhaps there was so little reference to Steve's past because even he didn't know what it was. They sent him on a quest to discover his missing history. Eventually writer Steve Gerber uncovered Steve's pinko roots:
None of this jives with the history of Steve Rogers found on Wikipedia or in other stories I've read, so I'm guessing this all got wiped out at some later point in time.
Postscript: It sure didn't take Marvel long to disavow this origin. They published a letter is issue 233 raising several questions about these flashbacks, such as why was Steve Rogers depicted as not joining the army until after Pearl Harbor, contrary to earlier tellings. In response, Marvel wrote:
Yours is just one of many letters expressing concern and confusion over CAP'S retold origin that appeared in issue #225.
But probably nobody is more confused than [current writer Roger McKenzie]. Because it will be up to him, sooner or later, to explain the events that took place in CAP #225 to the satisfaction of Marveldom Assembled.
And he will too. Somehow. Some way. Because one thing's for sure. Whoever that was in CAP #225, it wasn't CAPTAIN AMERICA...