for me, "old school" means "traditional".
someone who trains old school could very well use pushups instead of plyo ball pass. and most of the old timers i've worked with talk about how all they did, when they were young, for the first 6 months was a jab. now-a-days too many coaches try to teach tricks too early.
There's a balance between the old and the new. as a new trainer, stick with the fundamentals for your team's foundation.
good luck on your journey and check out this FREE online book by a really solid new school coach with old school wisdom.