Underage performers are very rare. The main reason is, when they are found to be underage, all their movies become blacklisted and can no longer be sold or even given away.
The performers who are underage, tend to look older than they are, which is how they got away with performing underage in the first place.
Far more common are performers who are of legal age who LOOK underage.
It is ironic that the true underage performers don't look underage!
Pedophiles are interested primarily in performers who are underage. It is a fetish that I don't understand. I don't understand a lot of fetishes such as scat, abuse, feet, etc. I can't recall seeing any performer under the age of 16 which interested me. I look for performers in good shape, attractive, energetic, enthusiastic, know what they are doing, enjoying themselves, etc. Very few performers meet that criteria until they are in their 20's.