Classic rock is a specific fucking genre! Eminem will never count. Slayer will never count. Black Sabbath will never count. Miles Davis will never count. Age has nothing to do with it.
Aerosmith's output circa 2000 is classic rock, but it was classic rock at the time. It was classic rock when it was new.
This is aggravating only because it's the same stupidity as using "new wave" or "modernism" to refer to, just, whatever's recent. It is a complete failure to understand how labels work. Linkin Park can't be classic rock for the same reason it can't be traditional blues, folk music, or classical. These words do not just mean... old.
The only reasons people say this shit are (1) simple mistaken ignorance, (2) stupid trolling, or (3) radio stations insisting the only categories of music are "classic rock," "R&B," and "country." Like ClearChannel trapped them in a timeless expanse by playing "the best of the 80s, 90s... and today." Today being the last twenty years.