Learn 有 + 几 + …？ and 多大了？/ S + …岁。 through Asking About Family and Age.
Examples
我弟弟今年十岁。
My younger brother is ten years old this year.
Examples
今天还是昨天？
Today or yesterday?
他还是学生。
He is still a student.
Examples
你几岁？
How old are you?
现在几点？
What time is it now?
Examples
他是医生。
He is a doctor.
我去看医生。
I'm going to see the doctor.
S + 有 + 几 + …？Use 几 to ask about a small quantity (usually under 10). This pattern is used to ask how many people or things someone has.
你家有几口人？
How many people are in your family?
他有几个哥哥？
How many older brothers does he have?
S + 多大了？/ S + …岁。Use 多大了 to ask someone's age (usually adults or teenagers); for young children use 几岁.
你的孩子多大了？
How old is your child now?
我二十岁。
I am twenty years old.
Two friends, Xiao Lin and Xiao Nan, are talking about their families.
小南，你家有几口人？
Xiao Nan, how many people are in your family?
我家有五口人，爸爸，妈妈，哥哥，弟弟和我。
There are five people in my family: dad, mom, older brother, younger brother, and me.
你的哥哥多大了？
How old is your older brother now?
我哥哥二十岁。他是大学生。
My older brother is twenty. He's a university student.
你的弟弟呢？
What about your younger brother?
我弟弟八岁。他还是个孩子。
My younger brother is eight years old. He is still a child.