In Canada (British Columbia at least) the legal age for being able to purchase and consume alcohol is 19 years. Unlike the states, you will only be asked to provide proof of ID if you look younger than 19.
Once is a fluke, twice is a charm it seems. I am very flattered that I have been asked twice now in the past couple of years to show my ID before I was allowed to walk out with some wine. Last time I asked the cashier whether she thought I looked too young; she said yes.