This is my third or fourth summer on my current bike, and so far it has only had a single flat. So, IME, 1.5-2 years is about average. I'm probably due.

Aside from a brief spate with my mountain bike when the rubber was cracked and every fleck of gravel would cause a flat (took me a week of this to get around to replacing the tire), I've never found flats to be a big problem, or even an annual problem.

If your route takes you to places that would take a long time to walk out of and access public transit or a ride, it's worth picking up a flat kit and learning how to use it. If you can just lock up until you have time to take the bike into the shop, then you're probably good.

My flat kit has more experience fixing other people's tires than my own.