I've found (like every other parenting thing), the less you stick to a "method", the easier it will be.
My LO started with sweet potato, banana, avocado...soft foods she could pick up herself. However I did not limit it to...
My DD is only 11 months old but I only wash her hair maybe every 2 weeks. Generally if it stinks and only then.
I don't think a lot of hair washing is healthy, though. I wash my hair FAR less often than most people do.