What constitutes being "old school" in the military?

Well, when I went to boot camp (Great Lakes, Co 312, 1959), I was issued a flat hat (never wore but required for seabag inspections) and a white seabag. I'm sure someone can top that, but not many!

Did you use M60A1's in your unit, instead of them being lawn ornaments at the local VFW, you might be "Old School". If you opened a box of C rations in the field, and they had Lucky Stripes in them, you might be "Old School". That's two from my career I can think of.

In my case. I came into the Army at the end of the 'Brown Boot' Army. Several of our troops were issued 'Brown Boots' that had to be re-died- black.
We didn't have 'jogging shoes' or PT gear to do our PT in. We took off our 'blouse' and did our PT in our Tee Shirt and pants with combat boots on. We did the 'daily dozen' exercises, including the horizontal ladder, pull ups and the 25 meter low crawl and don't forget the 'run dodge and jump' exercise along with the hand grenade throw to the 'bulls eye' ring.
Our Back pack was the LBE with butt pack and our shelter half and bed roll rolled up and wrapped around the butt pack.
M-14 basic issue, M-16 was still being tested and starting to be issued.
No Night Vision goggles, just the star light.
Everything in canvas not light weight poly material.
The DI could get in your face to get you to straighten out. No such think as pull you 'snibble card' when you felt 'pressured'
If you remember this, then you were 'old school'.

IN THE NAVY OLD SCHOOL WAS CONSIDERED AND CALLED ( ROCKS AND SHOALS ) THIS WAS WHEN DIFFERENCES OF OPINIONS WERE SETTLED OUT BEHIND THE AFTER STACK ON A SHIP, WHO EVER WALKED BACK WAS RIGHT.. THIS WAS FROWNED ON AND WAS DONE AWAY WITH LONG BEFORE I WAS IN THE NAVY. NOW IT IS THE SAME IN ALL BRANCHES NJP OR CAPTAINS MAST IS HELD FOR FIGHTING AND HORSE PLAY. ET

Standing watch in the engine rooom
Dungarees & chambray shirt as you work uniform.
Watching 35mm movies on the mess deck.
Having a service number.

I was US Navy from the time I joined in 63 while in my junior year in high school as a reserviist to evade the draft and I retired in 91. 4 years active and 24 yrs in the reserves. First active duty cruise after A and C schools was an around the world cruise on an old tincan that had been built in 44 to keep up with then fast aircraft carriers and heavy seas. Earned my sea legs during a typhhon in the pacific and a hurricane in the atlanic during that cruise.

You're old school if you're on your 3rd PT uniform, 2nd dress uniform, 4th battle uniform, 4th armor vest, and you actually had a chance at the extended scale for the APFT (hint, it went away like 15 years ago)

I trained on the M 14. Just days before leaving for Vietnam, I was trained at teh firing range on the Colt M 16.

The line fades w each generation- Ran PT IN BLACK BOOTS still drunk.Took the old PT test (run,dodge jump, crawl etc.....wore the banana PT briefly. Wore “Pickle suit” fatigues, wore jungle fatigues. TWs, Had beer machines in the day room. Custer’s Terrace dancing girls Ft Benning. Jumped out of “Huey’s”, 124s, C7s, Drove jeeps (M151A2). Jungle School in Panama. Duty in Italy and “West” Germany. Tec tapes (useless) BTMS, C rations, P-38 on my dog tags.
Highly Shined Black jump boots, breaking starch. No women in Divisions. Navigation by map n compass. Stood guard mount/duty. Area J (LTA) gas chamber. Pabst Blue ribbon. Smoking. Saturday inspections. Spec 4s, 5,6... . Shining boots n brass Every day/Week. Steel pot. No AWOL jumps. ARTEPS , REFORGER, LTA, FTX. Commissary made you place like items on the belt at check out registers. Ate in a Mess Hall NOT called a DFAC. WWII barracks. ZERO NEED FOR SENSITIVITY, diversity or trans gender training, we were all soldiers and most understood race creed n color don’t matter, we were ALL OD GREEN. No one had to tell us to look after soldiers and their families. Maximum effective range of an excuse; ZERO METERS. GI Parties.
Wall to wall counseling for those who didn’t get it or didn’t want to get it.

I ate C rations till 1983 and wore kakis till that year as well, Ja. I also wore fatigues And for field purpose wore camis. Year laters they were called and officially wore them till 2003 BDU’s Helloooooooo