It's for real brother and someone older than you ,someone you respect. or in a joking way.
In the office if a senior staff help you done something ,you might say:" 王哥,真是太谢谢你啦!"in this sentence, ge is just mean to be close.
A famous joke is "信春哥,不挂科" (Believe brother Chun, you can pass the exam),chun is Chris lee,and she is a tom boy.