What constitutes being "old school" in the military?

The real deuce and a half, Willis jeeps, and canvas shelter halves. The old BDU uniforms and black boots. Oh those were the good "OLD SCHOOL" days LOL.

And more old school still
Ate C-rations (especially heated over C-4) and learned how to avoid the unwanted meals (like ham and eggs), even when the carton was opened from the bottom
Had a copy of the Tabasco Charley Ration cookbook
Called your quarters a hootch and the local maid a mama san (even if she was Vietnamese)
Shaved in cold water in your steel pot, also useful for sitting when the ground was wet or muddy
Tried to get your AN/PRC-6 (walkie talkie) to work when you needed it
Know what a "slick" is

Heating "C Rats" over a chunk of C4...

How about standing guard on the boarder between east and west Germany!

If your E-2 pay was less than $100 a month.
Lived in open bay barracks that were built for WW II.
Ate C rations
etc. etc. etc.

Using an M-1 or M-14 Garand instead 9of an AK-47.

Anything prior to the current regimes 'woke' and gender bullshit changes now being forced on military members.

Probably already mentioned the Lister bag! Int any good unless it has miss growing on it!

Any period of time at least 10 years prior to your service time.

If you didn't wear woodland cammies in the USMC, you aren't old school.