@ Ixarku
I think your dad is like me & prefers the firmness of bananas when they are on the greener side ... then again here in Hawaii there are a few cooked dishes that are made with green bananas.
I'll have to ask him again if it ever occurs to me. When I've asked him before, he's always said that he just doesn't like them when they're ripe. Not really sure if it's the texture or the taste or the firmness of the fruit that's the issue.
Of course, my dad also likes sardines with mustard, macaroni and cheese with ketchup on it, and can't properly tie his shoes. He's never been diagnosed with any disabilities, and he's normal enough that you wouldn't notice anything weird about him in casual conversation, he's just always been slightly off-center compared to the rest of my family.