People aged 20-35 can be called elder sister, because they are young people, so they can be called elder sister completely, and people aged 35-50 can be called aunt. This means that 35-year-old people say that if you are older, you will see how old the gap between you and your partner is. Older than you 15 years old can add your sister, older than you 15 years old.
According to the standard age of men and women in China, 22-24 years old. Anyone older than you should be called uncle and aunt. People younger than you can be called elder sister or elder brother.