1. After the verb BE, say ‘Be + number’ or ‘Be + number + years old’; e.g.

Rohit is almost twelve.
= Rohit is almost twelve years old.

INCORRECT: I’m at the age of 22.
CORRECT: I’m 22. OR I’m 22 years old.

NOTE-I: Do not use AGE and YEARS OLD together. The usual way of mentioning someone’s age is ‘Be + number’; e.g.

She’ll be sixteen next August.

INCORRECT: His age is about fifty-five years old.
CORRECT: He’s about fifty-five. OR He’s about fifty-five years old.

NOTE-II: Say ‘Be my/your/etc. age’ or ‘Be the same age (as somebody’s)’

a) When I was your age, I was already in a sort of job.
b) Most of my friends are the same age as me.

INCORRECT: Soon you’ll be of my age.
CORRECT: Soon you’ll be my age.

INCORRECT: I think we are at the same age.
CORRECT: I think we are the same age.

2. Phrases with AGE as their main word usually begin with AT (not IN); e.g.

INCORRECT: In the age of 18, you are allowed to drive a car.
CORRECT: At the age of 18, you are allowed to drive a car.

INCORRECT: My father left school at aged fourteen.
CORRECT: My father left school at fourteen. OR My father left school at the age of fourteen.

3. When you mention two ages after a noun, use the following:

Aged + number + and + number         or        Number + and + number + years of Age

INCORRECT: They have two children in the age of 8 and 12 years.
CORRECT: They have two children aged 8 and 12. OR They have two children, 8 and 12 years of age.

4. When you mention an age range after a noun, use the following:

Aged + number + to + number        or        Between the ages of + number + and + number

INCORRECT: These books are for children at the age of from 4 to 6 years.
CORRECT: These books are for children aged 4 to 6. OR These books are for children between the ages of 4 and 6.

For more chapters/topics on English Grammar read the following book authored by me.

Link for buying the above book

For English Practice Sets on various topics read the following book authored by me.

Link for buying the above book