I think every child is different of course.
Mine is 3 1/2, he is starting to get into the figurines of Power Ranger, GI Joes, etc.
He doesn't know the difference yet,he just calls them all army guys or Spiderman, or Heros.
But, I will not let him watch the show. He is a VERY visual kid. Just from watching Jimmy Neutron, which he loved, he was very aggressive. With children learing how to play and socialize, especially for a boy, I don't want to "enforce" that side of him.
Also, if he starts watching those shows, he will get bored with the Disney cartoons, and Noggin, etc, that he right now loves!
When he is older maybe we will reconsider.