It's all countries you have lived in for 6 months or more cumulatively since the age of 18.I think you should get the police report as long as you’ve lived in a country for more than 6 months. I don’t think it has a cut off to say if it was 10 years ago or 20 years ago.
I can’t answer the part about working experience if it’s necessary.
https://www.canada.ca/en/immigration-refugees-citizenship/services/application/medical-police/police-certificates/about.html
regards