“Classic” Rock, as a term, is a bit of misnomer. Rock isn’t a language that no one speaks anymore. Rock music is ageless, organic, hardworking, vital, and speaks a language that everybody understands, and sings along to.
That said, there is something about the music of the late ‘60s and early ’70s that defines guitar-based rock — a driving energy and unprecedented songwriting that really warrants the term “classic.