From what I've heard, only Geiko can have Danna since Maiko are too young and inexperienced to become independent with a Danna, also it's rare these days that a Danna is a single person, generally modern Danna are a group of people who support the Geiko with her finances, basically they're like a "Fan Club" Who put their finances together to support the Geiko ^^ But I may be wrong.

There are cases when a maiko has had a danna too, for example former geiko Ayano of Gion Kobu had a danna in her maiko stage :) Yes,there are also ”fan club” type of danna, or a husband and wife being a patron of a certain maiko, I think you can see a similar example in Mamehisa’s erikae documentary.