表达“在十岁的时候”有哪几种？

when i was 10 years old

1.at 10 years old不对,应为when he is ten years old(用其它人称如有必要需改be动词形式)
2.at the age of 10是对的
3.其它用法:
when he is 10 year old
at 10如:You can retire at 60. 60岁时可以退休。
be 10如:I learned to swim when I was six.我6岁时学游泳。

正确,还有at 10-year-old.

at 10-year-old