I am 25 years old.

She is 32 years old , living in beijing alone.

她32岁了独自住在北京。

2. turn ...满...周岁

When I turn 30, I am going to have a baby.

当我三十岁时，我将会要个孩子。

Yesterday was my birthday , I turned 18.

昨天是我的生日，我满十八岁了

3. in one's 20s/30s/40s 

在某人20多岁时、30多岁时、40多岁时

I am in my 20s ,I just moved here a couple of months ago.

我现在20多岁了， 我前几个月刚搬过来

He is already 50s when he started his business.

当他开始创业的时候他已经五十多岁了

4. in one's early 20s , in one's mid 20s , in one's late 20s

在某人20岁出头的时候，二十五六岁的时候，快三十岁的时候

At the time , I was in my early 30s , I wanted to do something that would utilize my creative capabilities.那时，我三十多岁，我想做一些能发挥我创造能力的事情

You look quite young , you must be in your mid 40s.

I am in my late 40, I am still single.

5. at

He became a doctor at the age of 27.

I should guess her age at about 35.

He became a popular at an early age.

6. in one's teens 在某人青少年时

She is in her teens

7. above 30.. ,below 12..30岁以上，12岁以下

The style is very popular among women below 40

这个款式非常受40岁以下的妇女喜欢

This move is only for people above 16

这个电影只适合16岁以上的人看