I have to admit I find it a little odd to be called by my first name by someone who I've never met. It is especially annoying to me because I go by my middle name so it sounds really weird when someone calls me John.
On the other hand, I have no problem being called Andrew at my local comic book shop, but I am a regular there and they know me.
As to referring to your elders as Mr. or Mrs., that was certainly the case when I was a kid growing up but it is not something that has carried over into my adulthood. I always introduce myself as Andrew to children and don't expect them to refer to me as Mr. or Sir.