Noelle is right, humans 23, vampires 25 and Renesmee and the wolves 24.
I see your point, about Nessie being a werewolf, but really they are both halves of two species (Jake - wolf and human (?) and Nessie - vampire and human). About the Jake thing, I know he is part human, but there is another part, supernatural, that I guess is wolf, but perhaps is shape-shifter? I do not know, I am obviously no expert on these things.
But no, Nessie is not a werewolf, just like Jake is not a vampire.