Bob Atkinson,
I grew up with the Vietnam War. 
In 1965 I was a teen who knew where Vietnam was. I knew about the French.
I was knew of Cambodia and it's politics.
Not many American teens knew that much at that time. 
It was one of the topics of the '64 election.
My husband (I met in 1973) was a 19 year old from a small town who served there 1969 to 1970. Prior to that he never had heard of Vietnam or where it was.
In 1969, I lived in Hawaii, worked at the airport and saw young Americans soldiers on their chartered flights to Vietnam and back. Yes, I did know there were young Americans who fought and died there as well, dated a few, went to high school with some of them. 
The average age of those fighting in Vietnam was 22, not 18. 
The majority of POW's were older because many were pilots shot down or were officers  (majority were Navy or Air Force). Ron Ridgeway was the youngest POW.
My cousin was a Navy jet pilot who flew missions there too.
http://www.nampows.org/nampowslist.html