what kumirei said
EDIT:
お兄さん young man (or around your age)
お姉さん young woman (or around your age)
おじさん man (around your parents age)
おばさん woman (around your parents age)
おじいさん old man (around your grandparents age)
おばあさん old woman (around your grandparents age)
i may be wrong, they may just be rough ages not related to you… anyone?
especially because calling people “you” in various forms can be seen as rude, without knowing their name it is considered more polite to call them a familial name