My dad used to get his hair cut every two weeks weather he needed it or not.  He and his friends went to the same barber, so i think some of it was a meeting place for him and his friends.  Me, i have not had my hair cut in years.  At least 12 years or more, hehe probably longer. I am a old hippie.  I like long hair on everybody

if it's longer, every two weeks... if it's cut shorter then every three weeks to one month. it looks best when i cut it more frequently, though.