The safest answer is: Yes. There is a very strong derogatory flavour often associated with the noun-as-adjective. According to this article from The Age:
To say something is "old school" has become a pejorative [usage]. It
implies out-of-date thinking.
This association is not guaranteed to be assumed by a listener or intended by a speaker, but the term should only be used with great caution, carefully thought out contextualisation.
If one includes the views of the former Google Dictionary, the situation with connotations is seen to be bipolar:
old school: used, usually approvingly, to refer to someone or something that is old-fashioned or traditional.
But better safe than sorry (and I suspect that a younger audience might rather assume the pejorative nuance).
I once complimented a speaker on the way he communicated in such an acceptable, gentle (though not weak) manner. It's hard to give compliments without sounding mushy or patronising (I find). However, my 'You're an expert at hedging' wasn't exactly the best way I could have phrased it.