That's not surprising. I'm sure there's plenty of "oldies" that kids don't know. Yes, Hall and Oates are now considered "oldies".
Metallica's first demo came out 30 years ago. Next year, Kill Em All will be 30. Worse yet, The Black Album (Metallica's last decent album) came out 21 years ago. 21 years! I remember not being allowed to buy the album on Compact Disc, so instead I got a dubbed cassette copy of And Justice For All from the neighbor kid instead.