However, so much time has gone by that if someone from vietnam era was going to go on a shooting spree you would have thought it would have happened way before this.
I essentially agree with you, but the point here is don't assume the shooter is younger than 55, as an example. While someone in his 50's isn't likely to do well in an infantry unit he can still have lethal skills. If the police are trying to profile the shooter, keep the age options open, was my point.