Decrease in recognition rate

When recognizing 10 white middle aged people with "dnn_face_recognition_ex.cpp" of dlib, all were correct. However, even for white middle aged people, the recognition rate gradually decreases as the number of white middle aged people is increased to 100, 200, and 300.
Is this my way of testing wrong?
Or is it a limitation of resnet_model?
does anyone know the answer to this?
thank you.

[davisking]

That sounds right. The training data for this is sourced from images of American celebrities mostly. Which are unusually young looking and good looking people. So it totally ends up not working as well for more normal people.

[Cydral]

FYI, I'm trying to work on a version 2 of the model, with better database balancing... and a fine-tuning capability for those who want it.