I was 11 and my NT sister was 14 when 9/11 happened.
I was beginning my middle school years and she was beginning her years in high school.
When I arrived at my school, a message was said over the intercom in which my school's principal said, "Two planes have crashed at the World Trade Center in New York City and another has crashed into the Pentagon in Washington DC. However, there is no threat to Portland, so please go on about your day."
We knew what The Pentagon was for, but hardly knew anything about the WTC.
When school finished for the day, our dad showed up and drove us back home as quickly as he could.
When he turned on the TV, we were just shocked that all channels were showing coverage of what happened not only in New York City, but also Washington DC. Later of course, coverage was shown of the plane that crashed in Shanksville, Pennsylvania.
@ OP: You certainly are right about everyone whose birthday is September 11th. How would they certainly feel about telling people their birthday your guess is as good as anyone else's.
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Silly NTs, I have Aspergers, and having Aspergers is gr-r-reat!