I think some 80s rock music can be considered classic rock, but this was around the time when alternative rock started to take over, and the artists from the 70s who made albums in the 80s started to sound outdated. Punk can't really be considered classic rock in spite of beginning in the 70s. You could have some 90s bands that are similar to classic rock, like Pearl Jam or Soundgarden, but those are grunge bands and is considered part of alternative rock. I would say the heyday of classic rock would be from the release of Revolver to Physical Graffiti.