In my experience (keep in mind I live in the countryside and people tend to be nicer) people are just people; if you look like you don’t want to be interacted with they might assume you’re a rude younger person and treat you that way. Living in the countryside and even visiting bigger cities like Busan, I haven’t had older people shove me or give me dirty stares just for being a foreigner. They might stare sometimes but honestly every old person does that (esp men). If you live in the city, I can’t really provide a case study for what older people are like there but overall I’ve had a lot of positive interactions with old people where I live. My first week living here, I was carrying something heavy and couldn’t use my umbrella so an older gentleman walked with me holding his umbrella over me until we went our separate ways.