Instead of: "Hey, are you an intern/graduate student/post-doc here?"
You can ask: "So, what is your position here?"
Or, instead of: "Is this your first job after graduating college?"
You can ask: "How long have you worked here and what have you done before that?"
So that I don't have to say - again - that I am not an intern, this is not my first job and yes, I do look kind of young but that does not take away from my credibility, if you first clear you mind of all the assumptions that live there.