For those who haven't read the book "The True Meaning of Smekday" (which is the book this movie is based on), Tip is about 12 or 13. There is an explanation for why she drives even though she isn't 16.
I really shouldn't be watching Vihart when I'm sick and tired and disoriented. I watched this and sat there with my mouth open for a while trying to figure out what the heck I just witnessed. Amazing to learn about (when you aren't sick and tired and disoriented).