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I think Antiquated Linguistics might be closer, Totally Radical is more older people using/attempting to use younger slang.
There's also Disco Dan, if said hippy is still acting as if The '60s never ended.
"The only thing which is certain, is that something will happen".If the character uses outdated slang and other characters, in-universe, find it jarring or weird, that would be Speaking Like Totally Teen. An Aging Would-Be Hipster is someone likely to engage in this.

Is there a trope for when someone uses outdated expressions or slang? An example would be an aging hippy still saying "far out," and "groovy."