Right, I'd think that large age gap might be the biggest reason. Im only concerned with this generation bc I know older generation use honorifics more commonly. But here is the thing, one of my oppah is 11 years older than me, and he was fine with me using 반말 but I just felt really uncomfortable bc I felt like it was showing disrespect. He is like a sunbae to me but he told me to call him oppah Instead after the second time I met him. So..when I think I got the pattern it doesn't seem to apply lol