Expressing "age difference" with "da and xiao"
If you have siblings, Chinese people will often ask how much older or younger they are by saying: "他（她）比你小几岁" or "他（她）比你大几岁 ". Notice, here you can't use “年轻” or "老“.
A + 比 + B + 大 / 小 + Number + 岁
Note that 岁 is used here, instead of 年, to mean "year old."
- 我 姐姐 比 我 大 两 岁 。My sister is two years older than me.
- 你 比 你 哥哥 小 几 岁 ？ How much younger are you than your elder brother?
- 他 女朋友 比 他 大 十 岁 。His girlfriend is 10 years older than him.
- 我 老板 很 年轻，只 比 我 大 三 四 岁 。My boss is very young. He is only three or four years older than me.
If you just wonder which is elder or younger, these example sentences will be helpful:
- 你俩 谁 大 ？Who is older between you two?
- 你 爸爸 和 你 妈妈 谁 大 ？Who is older, your dad or your mom?
- 你们 五 个 人 里 谁 最 小 ？Who is the youngest among the five of you?
But if you're talking about being the same age, use this structure instead.
A + 和 / 跟 + B + 一样 / 差不多 + 大
A few examples:
- 他 女朋友 和 他 女儿 一样 大 。His girlfriend is about the same age as his daughter.
- 我 爸爸 和 妈妈 差不多 大 。My dad is about the same age as my mom.
Multiple Ways of Asking about Age
When asking about age with children, friends and elderly, there are certain things that you need to pay attention to. For example, children under 10, people your same age, people older than you, all have different ways of asking for age.
A few examples:
- 小朋友 ，你 几岁 了 ？Kid, how old are you?
- 大妈 ，您 多大 年纪 了 ？Old lady, how old are you?
- 爷爷 ，您 多大 岁数 了 ？Grandpa, how old are you?
- 我 是 90 的 ，你 是 哪 年 的 ？I was born in 1990. Which year were you born?
Sources and further reading