How old are you?意思是：你多大了?这是对年龄的提问.
可回答：I am + 年龄+ years old.或简短的回答：年龄+ years old.再简单点的可以直接回答：年龄.
例如：
---How old are you?
---I am 14 years old./ I am 14./ 14 years old./ 14.