What constitutes being "old school" in the military?

nowadays just drinking coffee is old school

smoke 'em if you got 'em.,,and have to give a few to guys without 'em.

Any service prior to 1993. I always thought that I served in 2 very different services. I experienced noticeable change around 1993.

If you have to ask....you are not "old school". In short though, it's someone who served and learned the processes before a new process/procedure/order came into affect. So, it is a moving line and depends on the topic of discussion.

Having enlisted 51 years ago during the Vietnam War :) I was "old school"! Yeck, I was old school when commissioned as a mustang. I even retired form the military old school.

Items not on the other lists, were some of the military social norms of the "old school" days. Just a couple. while in uniform" could not carry our small children (including babies). Also, we could not hold an umbrella with our right hand which for example placed my wife to be on the street side. And, we could not hold the hands of our wives / girl friends while in uniform outside a building.

All of that plus: green fatigues (purchased, not issued), khaki Class Bs (purchased, not issued), C-rats and "Elvis collar" BDUs.

Serving on a WWII Sumner Class Destroyer, USS Wallace L. Lind, DD-703
Wearing dungarees and boon dockers
Wearing Kapok life jackets during a re-fueling
No ear protection issued when in a 5 inch gun mount
Having to show a liberty card in order to leave the ship
Cinderella Liberty
No zippers on issue uniforms

Perhaps if you do things because they are the tradition of the Service. My Father was "old school" because he served pre-war (1938).

In simple terms being Old School is preferring the original method, process or procedure that has been changed.

"Old School" now probably refers to 1980s Cold War Soldiers when everything was about enforcing the standards, preparing for boards (by reading every regulation you had in the unit library), and conducting training constantly (including hip pocket training by junior NCOs in any slack time). The 70s, 80s, and early 90s Soldiers and junior leaders were much, much more knowledgeable about the Army and Air-Land battle and they did large scale exercises in Germany and Korea every year to test and practice that knowledge. Today's Soldiers don't learn regs because they can look up answers on their phones. They are also, for the most part, now "small wars" experts (counterinsurgencies) and have no idea how to operate in an Nuclear-Biological-Chemical environment. Nor do they know how to operate in an environment where we don't have air superiority or where there is a high threat from massed indirect fires or electronic warfare.