Not true in my experience. I've lived in five different provinces and I've never met a Canadian who uses Farenheit. I've never met anyone under 40 who knows much more than >100F = hot either.
Must be age-related, as you say. In fact, since they changed over in the 70's, 40yrold is about the right cutoff!
I wouldn't say so for celsius but I do find myself changing between feet / meters for certain things, like my height.
Quite the opposite for me. Fahrenheit makes no sense to me, it always sounds absurdly hot.