* Breaking Dawn Part 2 takes place a few years after Nessie's birth.
* Nessie's age is not explicitly stated, but she is still considered a child. She is described as having a playful personality and being very close to her mother, Renesmee.
The novel focuses on the immediate aftermath of Nessie's birth and the threat posed by the Volturi. It does not delve into her development over several years to teenagehood.
It's important to remember that the "teenager" trope is often associated with vampire lore, but in the Twilight saga, the focus is on the emotional and psychological aspects of vampirism, rather than solely physical changes.