I don't know when CASA decided to mandate it, but I certainly recall doing a CRM course as far back as 1991 or 1992 here in OZ and have done a few since.
The very first time I did CRM was in Holland, conducted by KLM sometime around 1980. After the Tenerife disaster they were among the first to come up with the concept of CRM. European operators were including it in most induction programs not long after.
Initially there was quite some resistance to the concept by some of the more 'rusted on' Captains of the day; often the same characters who never fully embraced the concept of sharing take-offs and landings with First Officers.