You're overly focused on iPhone vs. Android without considering all the other kinds of fanboism out there that simply go under other labels, whether it's patriotism, religion, favorite TV show, or brand of camera.
Is it all teenage boys? Well, teenage boys are a lot more passionate and vocal about whatever it is they're interested in than other demographics, but you don't have to look hard to find middle-aged Nikon fanatics, or Protestant nut jobs.
I don't think I actually mentioned iPhone or Android in my comment -- did you mean to reply to someone else?
However, I think you're excessively conflating different types of fanaticism here. Fanaticism about personal electronics, or TV shows, or brands of car, or brands of camera, is silly because these things don't fucking matter. Religious fanaticism, on the other hand, is fanaticism about something that is important. I myself don't believe any religion is likely to be true, but if I did, then this would be a sensible thing to get all worked up about.
The stakes of choosing the wrong camera are that you might wind up taking slightly worse pictures under certain circumstances. The stakes of choosing the wrong religion are (according to the tenets of those religions) that you'll get rewarded or punished for all eternity.
Likewise, patriotism can often be silly but at least it's about something important. If my favourite TV show ceased to exist it would be a minor bummer, whereas if my favourite country ceased to exist then I'd have some serious problems.
Is it all teenage boys? Well, teenage boys are a lot more passionate and vocal about whatever it is they're interested in than other demographics, but you don't have to look hard to find middle-aged Nikon fanatics, or Protestant nut jobs.