"Age" in this sense refers to a period of time in which a particular technology, or other pervasive social institution, is dominant in Society.

e.g., The Bronze Age, The Age of Reason,The Middle Ages.

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Note added at 2002-05-18 17:27:15 (GMT)
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Americans in the Information Age - U.S. Department of Commerce study examining which American households have access to telephones, computers, and the Internet, and which do not.
http://www.ntia.doc.gov/ntiahome/digitaldivide/
More sites about: Digital Divide > Falling Through The Net

Ennis: Information Age Town - includes business, community, and tourist information.
http://www.ennis.ie/
More sites about: Ireland > Clare > Ennis > Local Travel Guides

The Truth About Math Standards and Information-Age Math Reform
http://www.wgquirk.com
More sites about: Mathematics > Education

Information Age, Inc. - offering full turn key internet solutions.
http://home.the-information-age.com
More sites about: Georgia > Carrollton > B2B > Internet and World Wide Web

Information Age - information technology trends.
http://infoage.idg.com.au/
More sites about: Australia > Computer and Internet Magazines

Ben Li's suggestion is well covered the meaning of 社会信息化. But I think "Informatization" is created to cater this Chinese expression. If you do not want to do that way, perhaps you can re-arrange your sentence and translate the 社会 as a noun here, instead of an adjective and make 信息化to modify 社会, such as my suggestion "社会信息化 = information-equipped society".

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Note added at 2002-05-18 18:17:41 (GMT)
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Or another suggestion by following the same thinking path:
社会信息化 = information-based society