it's confusing because some people use it to describe a specific genre - old school = the original fast techno with lots of crazy breaks and cheezy pianos, which eventually split into hardcore and drum & bass. also known as "rave music". this sort of old school was made for a brief period of time, a long time ago, period.

but if you are using "old school" as an adjective, not a noun, then the key is in the phrase itself.

a "school" is a way of thinking. something doesn't have to be old to be old school - it just has to adhere to a way of thinking that is tried and true.

i noticed some big changes in the thinking behind and surrounding techno/trance that culminated in about 1998. the growth of the scene and introduction of virtual analog are largely to blame. out with the old, and in with the new!

but, things do come around again, and by 2002 a lot of records started to come out that harkened back to the old ways, and that trend goes on.

i would say that an acid house record produced in 2004 is infinitely more "old school" than a hard trance record produced in 1999, even though the later might be a "classic".