From Your Junior Brother to Your Senior Brother to Your Doctoral Supervisor

I was studying for my master's degree relatively late, around 28 years old. The person who greeted me on the first day of school was a boy who was five, six, seven or eight years younger than me. He was in his second year of graduate school at that time. I am obviously five, six, seven or eight years older than him, but he still calls me "little brother" and "little junior brother" every day in the college. Can you bear it? It must be intolerable! Concept: This is not a love story, love has a beginning