silver age

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A period of history secondary in achievement to that of a golden age.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun an historical period of great accomplishment in a field or a society, usually following, and not quite as good as, a golden age, and not as bad as an iron age.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (classical mythology) the second age of the world, characterized by opulence and irreligion; by extension, a period secondary in achievement to a golden age