My husband has straight hair he keeps in a tight fade, like nearly bald on the sides to very short at the top, and gets his hair cut every 2 weeks. I (lady, curly hair) can go a year between, just get it cut in short layers and let them grow out to long layers. The two of my kids who like theirs short but not crazy short go a month or two between.

Basically the shorter it is, the more you have to cut it - hair grows, on average 1/2 inch (13mm) per month, so mine has a 6 inch tolerance but my husband, with such straight and short hair, has a quarter inch tolerance.