A general question. I am interested in doing the above (not teaching skiing) but from my research it looks like anyone over 30 can't work for a few months in Canada. But the USA seems a bit easier.

I am 42 and was thinking of "doing" a winter in Colorado or BC. Any advice?

Look for a US ski resort that is able to sponsor H2B temporary worker visas. It should be noted these are for a specific company and you wouldn't be able to work for a different company on the visa.

These used to be quite easy to come by, 50,000 new H2B visas could be issued each year and people returning to to work for a company they previously had an H2B visa for did not count. G W Bush changed this near the end of his presidency and returning staff now count to whatever the annual quota is.

Upshot is fewer lift companies can now get the required authorisation as they must show that no US citizen is able to fill the job - this means it's more likely to be smaller or remote mountains that can get H2B visas for a wider variety of jobs. In most cases now such visas wouldn't be for entry level rolls and would be for specific skilled rolls such as experienced groomer drivers or fully qualified instructors.