Things will be a bit crazy, that is, if it is indeed that everyone owns some form of a gun.
If we consider 18+ to be "everyone" things might be considerably less crazy.
That is what some gun control laws try to do, though. Limit the amount of crazy people trying to get it and limit who is valid to own a gun "legally."
I'd seriously not want my 13-14 year old self to own a gun. And I'd seriously not want an emotional adolescent to own one either nor do I want a child owning a "real" gun. Strictly speaking, it is because some owners don't know how to take care of their guns from emotionally unstable people, and as a consequence, things get iffy at their home.