Typically, men should get a haircut every two to three weeks, but if you’re doing a tight fade (or something similar that needs extra detail) every two weeks should more than do the trick. Definitely no less than once a month as your hair is gonna’ get pretty crazy and out of shape if you wait that long.
Yes, you can go longer if you’re letting your hair grow out, but even when you are doing that you should still go in to the barbershop to get it shaped. You shouldn’t just wait till it takes a year for example to grow out, all the while your hair has been a disaster/shaggy/rough around the edges for the past 6 months or so…
So, in conclusion, try to go to the barbershop every 2-3 weeks, and if your like Aaron who pays very special attention to his hair, once a week works as well. It’s just a matter of how much time, money, and access you have to your barber. But, no matter what, never go more than a month without a haircut!