twenty, thirty, forty
She got married when she was thirty (years old).
It's thirty years old. (Key English Test; A2; Italian)
Most of my friends are in their thirties.
He was in his thirties and really handsome. (First Certificate in English; B2; Spanish)
They moved to Paris in the thirties.
In the beginning of the thirties in [the] USA the film industry [grew]. (First Certificate in English; B2; Spanish)