Commonalities with Magic in Fiction

Since it's hard to write a story where everyone in the world has awesome magic powers—isn't that like having ubiquitous technology?—authors write about individuals who become wizards or superheroes. They're special people who inherited their specialness. But if it's inherited, doesn't that imply superiority over everyone else? Even if the hero is nice and only uses magic for good deeds, well, their descendants might choose a different path. A world where less than 1% have inherited superpowers has dark implications. I'd like to see more stories that address this, and thoroughly explore the implications.

Manna, the One Source, allomancy ... a lot of fictional heroes require a specific fuel to power their magic. This defines the limit of their power. But aren't there are other ways to define limits to magical powers? Focus, for instance. One can only keep track of so many bolts of lightning or knives flying through the air.

Do you define limits of magical power for your character that's not tied to a fuel source? 

Magic ... at puberty. Or because of trauma. It's a common theme in fiction with supernatural, superhero, psionic, or magical powers. But why should this be the case? We all want to avoid magical babies, since those are dangerous, but I'd like to see magical manifesting that's more thought-through, and more creative, than "I got magic along with with my period."