A. How old are you?

B. I'm 21 years old.

A. What's your address?

B. 27 Main St.

  20     21         22         23           24
twenty twenty-one twenty-two twenty-three twenty-four

  25           26         27          28            29
twenty-five twenty-six twenty-seven twenty-eight twenty-nine

   30    40    50    60    70     80      90     100
thirty forty fifty sixty seventy eighty ninety one hundred