The flashback scenes did make Stormin Norman appear to be even younger next to his "veteran" actors. It is too bad that Chadwick is being overlooked for his role as their squad leader even though the ghost of Norman is present throughout the entire run-time of the film.
It was odd the way they sometimes tried to show younger versions of the actors and then sometimes, most of the time did not bother. At first it confounded me, but as the movie went on I ended up kind of appreciating it. It took me out of looking at the minutiae of the story and focus on the story. That is one big reason why the superficial aspects like the special effects did not bother me or even much register.
Whatever else the movie did that was good or bad the two things I respect it for and rate it highly for were:
1 - attempting and accomplishing was to put the Viet Nam war in historical perspective, but from the VN point of view and the "American Black GI" point of view as addressed by Hanoi Hannah on the radio, and ...
2 - then the story of Paul's PTSD. It was somehow very affective to make Paul a kind of irritating volatile pain in the ass throughout the movie, and then release in the last minutes was he had been up against and facing alone unable to talk to anyone about.