without thinking about it, I just called my server "sir" .... I would say he is less than half my age.

for me it is a form of politeness. very rarely have I ever gotten any sense that it was taken poorly. (I currently live in San Francisco)

that said I would not want to call someone something that did not want to be called.

but I also would love to live in a world where we routinely acknowledged the dignity of those we meet much more. Loosing this honorific would be a sad loss. Perhps we can invent a gender / age neutral one to replace them?