The movie is surely not old and not famous. I’m almost sure it was in English. As far as I remember, the girl had some problems with family and what she was going to do after graduation. She thinks she should stay in her home city to help her mother who struggled with alcohol problems. The girl meets a middle-aged man (probably an Asian), who came to her city to visit his relatives (maybe because his dad had died), they talk and become friends. This friendship helps her to make up her mind and go to study in a bigger city.
It took place in a small city in summer.
This probably isn’t it because some of the details are different, but have you ruled out Ghost World?
https://en.wikipedia.org/wiki/Ghost_World_(film)
No, unfortunately, that’s not it:(
“Adult World”?
https://en.wikipedia.org/wiki/Adult_World
Nope
Shanghai Kiss?
https://m.imdb.com/title/tt0469184/?ref_=m_nmfmd_act_26
No, that’s also not it T_T
Only movie with an adult becoming friends with a youth that I can think of right now is “Rushmore” (1998).
“One Crazy Summer” (1986), although I’m not sure if there were any Asians in there.