What constitutes being "old school" in the military?

If you did pt in you fatigues and boots and went to work right after that and your sgt was still able to lay hand on you when you screwed up like they did back in the 70's when I came in then you maybe old school military

If you ever:
wore yellow, nylon PT shorts
rode in a REAL deuce and a half
know what a gamma goat used to be
were transported in a cattle car
wore and washed in a steel pot
realized your M16 was built by the lowest bidding contactor
lived in WWII era barracks
thought the only definition of, "offensive" was "taking it to the commies"
actually put 2 shelter halves together to make and sleep in a tent
pressed your duty uniform
spit shined your boots Actually did 25 mile ruck marches up hill
ate Krats or MREs...

The list of required actions for "Old School" pretty much covers my time at Harmony Church at Fort Benning, GA.. We even watched them sink a Bradley in Victory pond demonstrating how they can cross water. Lucky they had that cable attached to it.

Did all that and still remember the 5 Event PT test, not to mention taking it! Just retired last year.

If you know what a shark attack is.
If you ever witnessed a SFC chew out a CPT (or a MAJ!), and the CPT back down because the SFC wass right.
If you ever saw a CO tell a 1SG to handle an NCO and the 1SG backed the NCO.
If you have ever taken a trip to the wood line for some developmental counseling
If you have ever thought to yourself that your NCO putting it on paper MAY have been more preferable....

Going through at least 2 major uniform changes.

One example I can think of right off the bat is when some of the older NCO's would call the NVGs (Night Vision Goggles) NODs (Night Optical Devices).

standing in line while on patrol on payday

C-rations, banana suits, hooched up with whores, murderous cadences, inflating five-ton tires without a cage, licensed to drive stick-shift deuces and Gama Goats and 151s and five-ton expando vans and 113s, MLRS rocket tracks that required hand-jamming every fire mission, MARS phone calls instead of internet, shelter halves, hand-cranked field phones, iron sights only, crackly rubber rain suits, SPIT-SHINED Corcorans, "no, Sergeant, it's not starch -- it's just Magic Sizing," shredding tons of Tac-Fire paper, the very first computers in a TOC (used only for very. slow. messaging), no "buffet style" chow choices in the mess hall that wasn't ever called a DFAC, regular and overnight passes (try not to get too drunk and "step on your pass"), nuclear artillery shells at the EAP facility, cleaning M16A1s without powder solvent, "FIVE MINUTES! SMOKE 'EM IF YA GOT 'EM!," no name tapes on Marines, no Gore-Tex on anybody, woolly-pullies, "Steam'n'Cream" bath houses, Quonset huts, a rifle stamped out by GM Hydramatic Div., Buddy Holly BCGs, downrange fist fights, rubbers at the gate in a box marked "PLEASE TAKE ONE," piss tubes, pile caps, berets actually meant something, guard mount armed with a mattock handle...

Male soldiers were issued Cackies for warm weather wear and Enlisted soldiers were also issued the Service Cap. If you were in the Army, you can remember seeing a Specialist Seven. Have driven a Jeep, M151A1 older version and know what a Willie was.