I shaved my head fresh out of high school, and cut my own hair for the next several years. Recently I got a Real Adult Job, where I'm at least a couple decades younger than most of my colleagues. In an effort to look more like a Real Adult, I got my hair cut by a professional. But I don't know what to do with it now that I can't just hack at it haphazardly any time the urge strikes!

So: how often should I get my haircut? I've looked online but the recommendations seem absurd (every 6 weeks, really?!), and I trust you guys more anyway. How often do *you* get your hair cut?

Edit: My hair looks exactly like this lady's, except less cross-stitchy and more real:

So, past shoulder-length, slightly wavy but mostly straight. I do not blowdry, straighten or colour it.