Sir

A student called me sir today and it kind of shocked me. I mean, I'm the same age as him. I'm more used to professor, teacher, or more often just my name. Don't get me wrong, it's definitely weird when middle aged students call me professor and bow to me. But most of the time it's just a sign of my position here and they don't have the English skills to be comfortable saying anything else. But sir?! This wasn't someone in a store being polite, this was a student that I've seen multiple times a week for months now. I told him not to call me that, and laughing, he asked if it made me feel old. I told him it did, but he said it's a position/title thing. I think he'll just do it on purpose now. I hope he doesn't tell his friends...