I am, now, 54. When I met my now hubby's parents when I was 48, I called them Mr/Mrs Hanson. Never even occurred to me to address them by their first names. We were ENGAGED for a year when I asked if I could call them by their first names. They were like, "YES! Of course!" But then again, I am not a meth using ex con so that helps.
Even when I was a little kid, all the neighbors were Mr/Mrs Smith, Mr/Mrs Miller, etc. When certain neighbors were like, "You are out of high school, call us Jim and Marie!" My response, in a stammering voice: "Uh, okay.......Mr Smith!" I just could not do it.