For the purpose of pretty much everything where it matters, a "new user" is anyone who doesn't have the remove new user restrictionsremove new user restrictions privilege.
If you have less than 10 reputation and post an answer to a question 30 days or more after it was asked, your answer is going to end up in /review. We'll dequeue it if your reputation exceeds 100 before the post is reviewed, mostly as a sanity-check to prevent lots of old answers from flooding the queues.
We can't base this on the user's creation date or even past activity, since this would allow posts from malicious or chronically-incompetent users to go unreviewed after a while.