Having in mind that this (28 mpg in city and 36 mpg at highway) would be an estimate of Corolla's gas mileage it seems that yours is above that spending range.
Gas mileage also depends on your driving style (if you keep your engine in right gears) and regular servicing (oil changes and types of oil are important for that fact).
Have in mind that there are special types of oil for engines that have crossed 150.000 miles or more that provide special protection of engine, and also oils which are designed to provide more economic fuel spending.
Well, seems to me that you took good care of your car!
www.fueleconomy.gov