I have sometimes wondered what would be the appropriate way of addressing (fellow) students that are junior to oneself. Given name? Full name? Name + 妹/第? Are there even cases where one can use 哥/兄 etc.?
I assume 小+surname is not used, is that correct?
And: does one have to take gender into account? I.e. boy addressing girl, boy—boy, girl—boy, girl—girl.
If one is not sure, how does one find out what the other person is comfortable with?