nineteen, twenty, twenty-one
space for twenty people
I think we were twenty people. (Key English Test; A2; Italian)
Most of the staff are in their twenties.
Teenagers and people in their twenties will enjoy themselves in the atmosphere of the rock-café. (First Certificate in English; B2; Russian)
I love the fashions of the twenties.
You can find the car [that] won the first car race in the world, [and] lost movies from the twenties. (First Certificate in English; B2; Spanish)