War is a young man's game - Why cast older actors?

Another factor is that to a 19 year old a 30 year old IS old and grizzled.

 

Fact: Assuming KIAs accurately represented age groups serving in Vietnam, the average age of an infantryman (MOS 11B) serving in Vietnam to be 19 years old is a myth, it is actually 22. None of the enlisted grades have an average age of less than 20. The average man who fought in World War II was 26 years of age.

Though you have a point Not just war movies. Sean Connery and Roger Moore as James Bond? or the 29 year old Oliva Newton John playinga teenager..

https://www.youtube.com/watch?v=7oKPYe53h78

 

As a genealogist I've been recently looking at draft cards and learned that there were a total of six draft registrations.
Prior to 1940 men enlisted voluntarily into the armed forces. The first draft registration took place in October of 1940 and recorded men between the ages of 21 and 36. The second and third registrations progressively widened the net in terms of age. The fourth "Old Man" draft was conducted in April of 1942 and included men between the ages of 45 and 64. These men were not automatically recruited into the armed services, of course. I wonder if any casting agent anywhere has taken this into account when working on a movie?

 

For Australians, 18 000 took the tour with 504 killed, the average age was 20...check out the Australian song "I was only 19" (Band Red Gum) - All about Vietnam.

 

Hollywood is less interested in historical accuracy than it is in the box office. Producers want a return (preferably a guaranteed return) on their investment, so they want bankable stars. Very few actors become big stars right out of acting school, and it may take several movies to reach that status. Most movie goers are used to suspending disbelief when it comes to the age of the actor, especially when the actor is well known.

 

From what I've read "fresh" troops tended to be a disportionate percentage of the casualties. If that is indeed the case then looking at the ages of those killed would produce a misleading indicator if projected onto the overall age of troops.