I'm 40 so I'm in a similar demographic to the
op
I was raised the same and my wife the same also. And we have raised our kids the same.
Rule of thumb for me is until the person in question corrects me it's Mr & Mrs etc, so much so my wife's grandmother has a friend every one calls him by his first name but as he was once my wife's neighbour she has always called him Mr... and as I and my inlaws all new him before they were friends we all call him mr... The trouble for us is he now says look you can call me by my first name but after him being mr for 15+ in my case and 30+ years for the inlaws it isn't a change that's happening quickly, besides, it still seems odd to have nan and bill nan and mr... Seems to roll off the toung better
That said though at our old house we had a lovely couple they were around the same age as my parents and they quickly asked us to call them by their Christian names, when my kids were born they were like the 3rd set of grand parents (the best people you could ever have living next to you) and they wouldn't hear of the kids calling them Mr & Mrs so they are the only exceptions to my kids