In Russian and English (and as far as I know Chinese) it's customary for kids to use honorific "uncle" when addressing elders by name (as a kid, you'd rather call an adult "uncle John" than "John", even if he's not your uncle).
In Russian, kids would also refer to a male stranger as "uncle".
Is is common across the languages of the world?
As a side question, is it ever used in languages which don't have a generic word for "uncle" (as opposed to "father's brother" and "mother's brother")? If yes, which "uncle" would they use?
Just to clarify, I'm not expecting a hundred of answers for each language separately. An ideal answer for me would be a reference to something like Greenberg's book which would already have aggregated the world's data.