I would say "formative experiences", see a Japanese and an English definition below:

原体験：人の思想形成に大きな影響を及ぼす幼少時の体験
(from Kojien)

Formative experience is the everyday life we lived growing up and the know-how we develop as a result. More often than not, the know-how develops beyond our awareness.

http://www.singlescafe.net/formative-experiences.html

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Note added at 48 mins (2007-12-06 02:29:48 GMT)
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Example sentences:

"For example, the formative experience of many of today's South Korean leaders was the Kwangju incident; for their parents it was the Korean War."
http://search.japantimes.co.jp/cgi-bin/eo20060126bg.html

"What makes a generation? Surprisingly the crucial criterion is not that its representatives are the same age. Much more important is that they share the same formative experiences.
These might be the shaking hips of Elvis Presley, Paris and Woodstock 1968, the provocative nihilism of punk in the late Seventies, environment concerns, acid house rave parties. …
...
The fact of living in such a heavily mediatised culture is a formative experience for young people everywhere on the globe."
http://www.maatismarket.com/category.aspx?categoryID=27

"The Phoenix Program was the assassination campaign in Vietnam that killed 40,000 civilians suspected of aiding the enemy. Phoenix was the formative experience for a generation of CIA and military intelligence personel, such as NSA general Michael Aquino and Col. John B. Alexander."
http://www.ziopedia.org/ja/articles/new_world_order/monarch/

"Yet they are responding less in the mold of their parents’ generation than their grandparents’. Why? Because 9/11 is the formative experience of this generation, and it is a different formative experience than that of the Baby Boomers’—probably JFK’s assassination."
http://www.familysecuritymatters.org/index.php?id=271463

"The former represents an older generation that opposed the monarchy and has 2 1/2 decades experience in national leadership. The latter represents a younger generation whose formative experience was the Iran-Iraq War..."
http://www.rferl.org/featuresarticle/2005/6/6840A374-8025-44...

"For instance, Strauss and Howe define the Boomer generation as anyone who doesn't personally remember World War II. They are different from the Silent Generation, who share the formative experience of childhood during the war."
http://en.wikipedia.org/wiki/Strauss_and_Howe