Yusuke, yes, that's right. It was a popular slang phrase in the US in the 1960's and 1970's, but not used much after that. It does sound too old-fashioned now to use seriously. A perfect Japanese translation is 'Sugoi', with the same meaning, used the same way, to express amazement/astonishment. Hope that helps!

I don't think it is dated. But that might be because I use it regularly ;) I tend to use it as a mild expletive, either to express frustration or wonder.

I see. it's an old expression! Thank you!

Meaning: probably a more current slang equivalent is "cool", but slang changes very fast https://www.urbandictionary.com/define.php?term=far%20out If you use this term today, it probably marks you as either non-native (OK, we can't escape that), or ancient hippy - a very good thing to be. Older people will understand.