DOROTHY: If happy little bluebirds fly beyond the rainbow, why oh why can't I?
A big part of the Coming of Age equation involves pushing against boundaries. That's why teenagers give grown-ups so many fits. Here, Dorothy's pointing out that she's really kind of had it with her drab little corner of the world, and ready to do a little growing up. She feels misunderstood and ignored.
SCARECROW: You see, I can't even scare a crow. They come from miles around just to eat in my field and laugh in my face. Oh, I'm a failure because I haven't got a brain.
This is kind of a childish complaint when you think of it, not because his concerns are illegitimate, but because he thinks his lack of brains are the problem. Trust us big guy: it isn't.
SCARECROW: Come along, Dorothy. You don't want any of those apples.
See what we mean? The Scarecrow has plenty of brains. He just didn't have anywhere to apply them in a practical context. Once he does, oh my does he bloom! Here, he cleverly finds a way to get Dorothy something to eat.
DOROTHY: Why, you're nothing but a great big coward!
An important step on the road to coming of age is seeing things for what they are, and realizing that they can't hurt you. Or, on a more practical level, speaking truth to power. "Hey I can see that you're lying to me and I'm gonna call you on it." It's a huge psychological milestone for a child when he or she sees that his or her parents are fallible humans.
COWARDLY LION: Well, wouldn't you feel degraded to be seen in the company of a cowardly lion? I would.
The Lion's being a bit of a little kid here, looking for excuses not to go on this trip. As is often the case, Dorothy gets to step up and be the adult: giving him "permission" to come with them to the Wizard. In a lot of ways, she's come of age already.
OZ DOORMAN: The Wizard? But nobody can see the Great Oz! Nobody's ever seen the Great Oz! Even I've never seen him!
DOROTHY: Well, then how do you know there is one?
This is a logical question, and we bet you've heard parents deliver some variation of it to their children. The only difference is that Dorothy's asking the question and the adult is the one caught in it. Another sign that Oz is full of children in need of some growing up.
DOROTHY: Oh, thank you so much! Now we can go back to the Wizard, and tell him the Wicked Witch is dead!
This really is Dorothy's definitive coming-of-age moment. Witch = dead. Prize = well in hand. Wizard = minor technicality at this point. Give this gal a driver's license and a voting form. She's ready.
DOROTHY: If you were really great and powerful, you'd keep your promises!
First case of her new-found adulthood officially in action: she calls out the Wizard's duplicity and seems ready to stick by it. We've seen flashes of it before in the story, but this is the first time it really sticks (with a little help from Toto, of course).
DOROTHY: Well, I, I think that it, it wasn't enough to just want to see Uncle Henry and Auntie Em, and it's that, if I ever go looking for my heart's desire again, I won't look any further than my own back yard. Because if it isn't there, I never really lost it to begin with! Is that right?
It's more than all right, Dorothy: it's right on the nose. Consider it your final exam before passing and getting your diploma.
DOROTHY: I think I'm going to miss you most of all.
Not every part of coming-of-age is empowerment and awesomeness. Dorothy's going to lose some things along the way… most notably her friends in Oz. Those losses are tough, but they're part of coming of age; a sad lesson that Dorothy mournfully accepts. We all have to leave behind our teddy bears and blankie when we grow up; that's one of the trade-offs.