How does Mama respond when Linder appeals to her after Walter tells him that they have decided to move into the house? Why is it significant?

MAMA: I am afraid you don't understand. My son said we was going to move and there ain't nothing left for me to say, (Briskly) You know how these young folks is nowadays, mister. Can't do a thing with 'em! (As he opens his mouth, she rises) Good-bye.

In this comment Mama defers to Walter's decision as the man of the house. This is significant because Walter has finally proved himself worthy of the title.