at the age of meaning in Chinese
我在15岁的时候
在岁的时候
在岁时
在……（多大年龄）的时候
在……年龄
在…几岁的时候
在几岁时
在某人多大时
Examples
- She was barely walking at the age of four .
她四岁时才勉强会走路。 - He was struck down by cancer at the age of thirty .
他三十岁时死于癌症。 - He ran away from home at the age of thirteen .
他十三岁那年就离家出走了。 - My sister started school at the age of six .
我妹妹六岁入学。 - Not finding yourself at the age of thirty-four is a disgrace !
34岁了还不得发挥，真丢人！