At what level can hard pen calligraphy be taught to students?

I think the key is that the teacher has a set of good methods, as long as the structure and strokes of words can be praised. In addition, if you are practicing pen writing, there are not many pen copybooks to choose from. After all, pen as a writing tool is only available in modern times. In ancient times, there were no pens, but there were many brush copybooks. In fact, brush copybooks are sometimes helpful to the writing of pen writing. You can find this article "How to choose brush copybooks for beginners' calligraphy (with the names of 46 classic copybooks)", which introduces some brush copybooks.