Xiao Sheng is used for general self-humility, which can be said to the elders, peers and even younger generations of strangers, but it must be in a young age and generally belongs to teenagers;

The younger generation is suitable for inferiority in front of the elders. Generally speaking, you should know that the other person is an elder or obviously older than yourself. As long as you are old, you should still call yourself a junior. It can also be used to humble yourself in front of unfamiliar elders.

Late students not only show that they are junior girls, but also show that they have a certain relationship with each other. Generally speaking, the other party is grandparents, father's generation, or teacher's generation. The person you respect most can be called a late student.

This is only my personal understanding, and thousands of experts and scholars have corrected me.