I started talking with my father about this in the context of ‘generations’ but since generations are an increasingly eroded concept, we just switched to our lives.
My father was born in 1952, and considered the most important events in his life to be from 1968-1974. More or less it went from the violence of the summer of ’68 to the resignation of Nixon in ’74. What he pointed out is that had he been a year older, he would have been in college when Kent State (for the non-Americans, this was a shooting of student protesters, four died) happened, and he noticed that those older than him were much more militantly political.
Personally, I was born in 1990. It is not September 11th that is reflected in my worldview, but rather that America has not known peace for over half my life, and almost all of what I remember well. For me and those of my age, war is not only in our minds, it is background noise.
I have for days forgot that the country of my birth has spent trillions in a war with no clear enemy. I am not alone for those people who are not, through family and friends, close to the soldiers that fight. If anything it is the chief difference between my father and I- I have lived through wars without a draft, and thus without serious, endemic opposition to the war.