When did u start letting DC watch superheroes?

DS has been dying to watch spiderman. He asks all the time - but I am just not in love with him watching it so early. Apparently all the kids at school talk about it LOL!. He definitely doesn't have the attention span for a movie so I don't even know if he will actually watch spiderman/batman/ etc. So, at what age did u let your dc watch this? I guess he is bored with Nick Jr and sprout which I would like him to watch until he is 21