Toph felt his heartrate jump momentarily and it makes her suspicious of the question about her age. She shoots him a warning look as she answers in case it's intended to go somewhere she doesn't like.

"I'm thirteen."

She isn't reckless; she especially wouldn't be reckless with her feet. Toph knows her limits and, sure, she constantly likes to push them and ride them to the edge, but that's what makes her great. Getting a toe frostbitten off would be not great. She doesn't need the concern and she especially doesn't need anyone treating her like a child.

The fact that she is one makes it really chafe.

As for the gross and dirty part, nothing brings her greater pleasure than laughing in the face of people who want her to act civilized. It feels incredibly cathartic absolutely every time.

"There's such a thing as pro heroes?" Toph laughs a little. "That's hilarious. You're right. If you have to wait for somebody else to tell you what you are, you've got a long way to go." She delivers this line almost off-handedly, but she feels it fiercely and means it deeply. Defying what everyone else has told her about who and what she is is basically her life's mantra.