No wait, at that point Hank Pym already had the Wasp as a sidekick/partner and Rick Jones had been introduced as the Hulk's sidekick and would later become Captain America's. So it was more a "no boy sidekicks with the same set of powers and abilities as the hero's" rule.
I think Stan thought Cap hanging out with a teen boy looked kinda gay. Batman and Robin can look kinda gay too.
Cap and Falcon didn't seem gay.
Jan was a woman
Hulk was more of a monster than a man
Reverend Meteor (and why didn't someone in the golden age ever give Toro a shirt!)