What did you call your boss? Or anyone your parent’s age? Was it Mr/Mrs - or Sir? There were class undercurrents - and context. It was a minefield where often the best solution was to avoid it completely, at the risk of the interaction becoming, well, odd. A general rule was more than twice your age and it was Mr/Mrs - and four times your age almost certainly Sir.
I feel for the war generation who are often, particularly in a caring context, addressed by their first name relentlessly when you can see that it irritates - but they are too polite to say so. But overall, first names are so much easier.
