old
1.习惯说How old are you和I do not know how old he is，不该在old前面加上many years。
2.a boy of ten years old, a boy of ten years和a boy ten years old都可以说。The boy left school at ten years old和The boy left school at ten (years)也都可以说。
3.可以说in old age，但不可说at an old age或at the old age of ninety，该把old改作advanced。
4.关于older brother等，参见elder