1.表示“整岁”,直接用基数词或year,age,例如“他20岁”可表示为:

He is twenty.
He is twenty years old.
He is a twenty-year-old man.
He is aged twenty.
He is at age twenty.
He is at the age of twenty.
He is twenty years of age.

2.表示“在某人几十多岁”,用“in one's +基数词复数形式”,例如:

他七十多岁。He is in his seventies.(从70岁到79岁之间)
她五十多岁。She is in her fifties.(从50岁到59岁之间)
还可以借助early,middle,late来表达得更明确一些,例如:
那女孩今年二十二、三岁。The girl is in her early twenties.
他今年十四、五岁。He is in his middle teens.
她今年二十八、九岁。She is in her late twenties.
 
3.表示“快满多少岁”用进行时或将来时,例如“他快满十八岁了”可说成:

He is getting on for eighteen.
He is going on eighteen years old.
He will be eighteen years old.
It will be his eighteenth birthday.

4.表示“不满多少岁”,用副词barely,nearly,al- most,quite,yet,just等,例如“她不满十七岁”有以下几种说法:

She is barely /nearly /almost seventeen.
She is not quite /yet seventeen.
She is just under seventeen.

5.表示“差多久满多少岁”用介词off,例如:

他差5个月就满19岁了。He is five months off nineteen.
她再过3年就50岁了。She is three years off fifty.
 
6.表示“超过多少岁”用介词past,例如:

他已年过50。He is past fifty.
他是一个过了中年的人。He is a man past middle age.
那孩子两岁零两个月。The baby is two months past two years old.