There is good fiction, there is good entertainment, and there is reality. The movie makers don't rely on customers who demand reality, knowing that fiction and entertainment will put dollars in the box office.
In most of the Vietnam movies I have tolerated watching the actors are usually 10 to 20 years older than anyone I saw in the field in Vietnam. Most of us in real combat units were 18 to 22 years old, even the company-grade officers were usually in their early 20's. Sure, there were senior NCO's and officers in their 30's, even 40's, but they were almost always in rear secure areas, not out in the weeds.
Drugs, and drug use (marijuana and heroin primarily) were common, especially among rear area and support troops. In actual combat units drug use was not tolerated at all. Not unusual for a doper to be beaten to a bloody pulp when caught using drugs in the bush or while on perimeter guard duty, etc. One way or another, dopers were shunned until transferred out of the combat units. Military brass did not want criminal charges or court-martials (adverse publicity) so the troops did what we had to do in order to safeguard our own welfare.
Most non-military folks don't understand that for every soldier at the sharp end of the stick there are a dozen or more troops serving in supply or support roles. Not every soldier who went to Vietnam saw actual combat, most served in relatively secure areas and positions. I'm not saying that as a criticism (I would have gladly traded places many times), I'm just explaining the realities of military structure and deployment in a combat theater.
My primary MOS (military occupational specialty) was 11F4P, Infantry Operations & Intelligence, skill level 4 (non-commissioned officer, pay grade E5-E6), paratrooper, with a sub-specialty as a Pathfinder. I went to Vietnam as a 18-year old Private First Class, promoted to Sergeant by the time I was 19 (generally responsible for 8 or 10 troops, nearly all my own age or younger). I went back to Vietnam a second time, got promoted to Staff Sergeant (generally responsible for 30-40 troops), and came home before I was 21 and old enough to vote or buy a drink in a civilian bar. I proudly display the Combat Infantryman Badge (google-search that, only one way to earn it), and I hold four awards of the Purple Heart Medal (turned down a fifth because it was USAF close air support fire, third gun run, and I was shooting back at the *** who wounded everybody in my team before he flew back to his air conditioned quarters in Thailand after his hour and a half in "combat"). Just about all of my "awards and decorations" (impressive looking display) arrived courtesy of the US Mail, months after I left Vietnam, and I can read the award citations without recognizing anything about a reported incident.
"Apocolypse Now" and a dozen other Vietnam-based movies are dramatized and fictional accounts, mostly produced in the aftermath of an unpopular military venture by anti-war, anti-US, anti-everything know-it-all types with no attempt whatsoever to present truth or reality, just drive the box office revenue while pursuing a political agenda.
Rant over, for now.