Once upon a time, I was looking forward to such a person. First of all, I am a boy and I hope my pen pal is a girl.
However, to be a pen pal with me, I have no other requirements. There are two points:
1. Good writing, at least some knowledge of classical Chinese, and familiarity with history and even philosophy.
2, the handwriting should be beautiful. I have taught calligraphy, and I don't want to receive a letter with uncomfortable handwriting.