My hair is long ( to the middle of my back) . It doesn't go greasy. So I wash mine once a week. As it's a pain to dry and straighten, and takes ages. I have come across several of my friends who also wash theirs once a week. I've heard it's good to leave it if you can. But wouldn't go longer than a week. No judgment if you do go longer than a week, it's up to you.
I'm just interested how often others wash their hair.