I have been hosting for less than two months, with only 6 sets of guests (each for a week long stay). Only one of my guests had a previous review. 4 of the other sets were brand new Airbnb members. The last set of guests had been members since 2016 without a review. All guests have been wonderful.
I agree with Ned & Laura. Start a conversation with them, and see how you feel. One of my guests, prior to booking, asked me why I did not have any reviews yet. So, maybe you could ask your potential guest, why they haven’t had a review yet. Maybe they joined last year, intending on taking a vacation, but were unable to.