In those days most people left school when they were only fifteen years old.
那时候，大多数人上学只上到十五岁。
He is ten years old.
他十岁了。
At thirty years old, he was already earning 40 000 a year.
他三十岁时已拿到4万英镑的年薪了。
You don't look 15 years old
你看上去不像15岁。
At 54 years old her energy and looks are magnificent
她54岁了，精力和气色都非常好。