(someone) is in (their) mid-(twenties/thirties/forties/etc.)

We often don't know, or don't care about, someone's exact age. If you want to talk about someone's age in a general way, you can say it this way:

She's in her teens.

He's in his early twenties.

She's in her mid-thirties.

He's in his late forties.

These can also be written as "20's", "30's", "40's" and so on.

This phrase appears in these lessons: