I'm curious, in which context does it matter? I know that this is a very cultural thing - as an example here in France it's completely unimportant, you would s

I'm curious, in which context does it matter? I know that this is a very cultural thing - as an example here in France it's completely unimportant, you would simply address kids (or at least younger kids) a bit differently than adults, but appart from that the age difference does not matter at all (and culturally it's important to know whether someone is a kid or not, because, to simplify, kids are legally "irresponsible", cannot vote, purchase alcohol, etc and some adults must have legal authority over them)