Ex-mas follows the story of Lila Beckwith and her quest to get her little brother back before her parents come home on Christmas Eve. He has runaway to save Santa - needless to say the tale is humorous.
Young Adult, YA, literature primarily focuses on protagonists 13-18. New Adult, NA, literature primarily focuses on protagonists 19-24. (Some may argue that NA goes up to 30, but, considering I read quite a bit of this genre, I think it is capped off by age 25.) These genres pertain to character development and transitional periods in their lives.