In general, the warmer the climate, the faster you have to change your air filter. The logic is simple, as warmer weather allows for more dust particles to float which in turn clog things like air filters up. Even stationary air filters on air-conditioning units get clogged up relatively quickly.
Your first clue if you need an air filter replacement is a drop in acceleration. You can also pop the air filter box in your hood open every so often to check if the filter is dirty. If you can't tell by looking, but it's been more than three years or 48,000km you probably should get a new one (especially if you can save money by doing it yourself).
However, you should be wary if every time you get an oil change the repair shop says you also need a new air filter. We would expect most drivers can go more than a year, at least, and probably more than two years.
If you have any suspicions or question, why not head down to your friendly neighbourhood Tayaria Service Centre.