Last I heard, you'd have to be 24 or under to get a true standby ticket in Canada. Standby tickets are applicable on domestic flights only. International flights, I'm not so sure. They are generally cheaper for sure, as I've used them when I was younger. But by how much, I honestly can't remember. I've never heard of true stanby tickets for business class, but it probably exists, yet the same age restrictions may apply.
But if you have upgrade coupons or stickers (both Air Canada and Canadian have them, I believe), you can even upgrade on a discount fare - that's where a standby applies, as you can't reserve an upgrade on a seat sale fare, but you can still upgrade on a standby basis. There are certainly no age restrictions in this case. I know this is possible, as I've done it a couple of times on CP aircraft.
Frankly, I think if you didn't show up for the flight, you'd lose the money, unless you had travel insurance (Travel agents hawk these all the time).