General swearing was mostly allowed at home from mid-teens but we always knew not to swear at people, in company, at school etc.
Swearing is absolutely no indicator of class, intelligence, education, etc (I know plenty of very posh, educated, intelligent people who swear like you wouldn't believe) as long as it's in the appropriate context.
Me in the office at work: "This website is fucked" - fine.
Me with a long-standing client who's a friend, are informal with one another, on the phone just catching up about a project: "Fucking hell, did you see X?" - fine, the context is there, it's a private conversation, I already know we're comfortable with that.
Me in a meeting with a big client who we're trying to impress: "I've fucked this slide up" - not fine, shows a lack of awareness of context, that's where I'd see it as inappropriate and crude.