Definitely not beyond 18 and good luck going after JB. There's still a substantial portion until early 20s, but by age 22 I recall it's around 5%. After that only those who actively safeguard their virginity remain. I've encountered some of them they seem to either:
a) have a severe phobia of men and so avoid them at all costs
b) are very religious and so refuse men who don't conform to their exact beliefs
c) are complete shut-ins due to insecurity, mental illness, etc. essentially the equivalent to many shut-ins on this forum
The latter category, "femcels" if you wish to call them that, I think used to be much more common before the internet. But now, even a woman who has never used a dating app will inevitably talk to men on social media, online forums, etc. and find a boyfriend that way. There might be some who don't use any social media but they're very rare.
I think the only other kind of woman who remains a virgin past her teens and early twenties are borderline autistic ones who become so entrenched in their career that they give no time or attention to men. Probably the most likely place to find such a woman would be in graduate school in one of the few STEM fields that has a lot of women, like veterinary science, biochem, etc. There may also be a small number who are complete hikikomoris and don't talk to people on the internet, but then there's no way you can find them. Such women are common in Japan (and much of East Asia) hence their high rate of female virginity. But in the West they are very rare. This is one of the few advantages that ricecels have.