I've personally found the older people to be the most friendly. That was one of the biggest surprises. Not sure how much of that is older people just being happier in general. This could totally be biased as the older people I interact with are either in a service role, or a wealthier traveler, which may be more friendly than the general population.
It's refreshing to see other foreigners not feel bitter about Japan. The subreddit of foreigners in Japan feels like a cesspool of people with this dogmatic view that Japan isn't like their home country
On the other hand, I've met a plethora of young people who've become friends I meet and stay in touch with.
Honestly the funniest experience I had with culture clash was one day at a hotel I stayed at in Takasaki. I got in an elevator occupied by a young family. As soon as I walked in, the little girl, maybe 6 or 7 years old, just dropped her mouth open, completely gaping at me the whole time we rode the elevator.
Probably not too surprising, assuming they're from Gunma or a similar prefecture that doesn't see as many foreigners.
That's the vibe I've been getting which did come as a surprise. I think the movies I watched (both Hollywood and Japanese) do a disservice to them - especially the ojiisan's.
That's not been my experience over the previous six years I've lived here. Initially I had a company sponsor me for a work visa but I've now got two relatively straightforward paths towards PR if I want it. Locals have been very accommodating and have bent over backwards to help me integrate into this society - that even includes the older generations.