Here is the message I just sent out to my friend:
I referred to the bartender as 哥哥, but the bartender saw my WeChat, and said the following (the exact sentence might not be same):
He is a bit younger than I (he is around 20 I think). And since I'm older than he, he said it is not correct to say 哥哥.
However, I asked then if it is OK to say 弟弟, but he said it is not OK in China to imply another person younger (which is insulting I think). So I asked again then what I should call you in the conversation with my friend, and he said he also seemed not to know the correct word.
He eventually said 朋友, though I asked again, the what I should if the bar is what I go to for the first time. He yet again seemed to struggle to answer my question.
Eventually, I asked if then it is OK to refer to him as 小哥哥, and then he said "随便你".
So my question is, in such situations where I must refer to someone who I know that is younger, how should I refer to him in the conversation with another person? Is 小哥哥 the correct word or is there possibly better word?