Probably '62 to '74. It is where ALL classic rock came from. Just leave the fraggling, soft-centred, saccharine, twee Beatles out of it. Without the bith of rock in that period there woud be no rock (as distinct from knicker-wetting pop)

A case could be made for the 20s/early 30s and American Delta music. Without that there would never have been rock'n'roll and hence no classic rock, but the groping for teen angst in the 50s and until the Mersey and London sounds of the 60s have no more claim to merit (and possibly even less) than Pulp, Oasis or Blur. The 40s and 50s gave us the Andrews sisters, and Johnny Ray. Enough said.

Some case might be made for Bob Marley and the Jamaican musical revolution. IMHO without the collision between that and Tamla Motown (and James Brown) there would be no current MoBO. Whether that is a good thing or not is another question...