What is a Modern Classic Car is a very subjective and debatable subject with no definitive answer.
In answer to your original question, the 350Z is not termed as a classic for insurance purposes.
This is a good read: https://drivetribe.com/p/what-defines-a-modern-classic-XHDlX2PJQH6KRLDhyn9nBQ?iid=ExJzKzv0S5yqTWL3HoT12A