Kat, Incorrigible by Stephanie Burgis

Lead:

I was twelve years of age when I chopped off my hair, dressed as a boy, and set off to save my family from impending ruin.

Ending:

I was twelve years of age when I cut my hair short, became a highwayman, and captured husbands for both of my sisters.
I could hardly wait to find out what would happen next.