In my edition, page 22 begins chapter 5. I don't know how much evidence you'll find for Scout's maturity this early in the novel. After all, she talks about beating up Dill at the beginning of this chapter because he "neglects" her after professing his love for her. The novel does reflect Scout's growing maturity, but most of that is shown closer to the end of the novel. I'd thus have to stick to her bravery from this section.
When they try to pass a note to Boo Radley, young Scout is used as a lookout and doesn't flinch from the responsibility:
The three of us walked cautiously toward the old house. Dill remained at the light-pole on the front corner of the lot, and Jem and I edged down the sidewalk parallel to the side of the house. I walked beyond Jem and stood where I could see around the curve.
“All clear,” I said. “Not a soul in sight.”
Here is young Scout, standing alone when she fully expects to face "Boo Radley and his bloody fangs," yet she fulfills her duty to the group bravely.
She also bravely questions the faith of the neighborhood which would condemn Miss Maudie to hell for spending too much time outdoors—while glorifying Miss Stephanie, who is the town gossip:
My confidence in pulpit Gospel lessened at the vision of Miss Maudie stewing forever in various Protestant hells. True enough, she had an acid tongue in her head, and she did not go about the neighborhood doing good, as did Miss Stephanie Crawford. But while no one with a grain of sense trusted Miss Stephanie, Jem and I had considerable faith in Miss Maudie.
It's a pretty brave move to consider Miss Maudie's character and thus reject the religion that has condemned her, especially at Scout's impressionable age. Scout thus shows that she understands the truth of real faith compared to a "faith" meant for the display and approval of the town.