Don't have any personal experience with this
, but this is what AC's FAQ says:
Q: Does Air Canada offer senior discounts?- These fares are not available for travel within Canada or between Canada and the US. Senior fares are offered for travel between Canada and Caribbean/Mexico/UK and USA to UK.
Typically, there is a 10% discount off of the base fare before taxes and surcharges. Senior’s discounts cannot be booked on aircanada.com at this time. For fare type applicability, fare quotes and reservations, please call Air Canada Reservations.