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Prepositions with nouns

Of age vs at age

Of age and at age have different meanings and grammar. Of age means legally old enough, while at age is normally part of a longer phrase such as at age 18.

Quick answer

When to use of age and at age

Use of age to mean legally old enough for an activity or responsibility. Use at age followed by a specific number to talk about someone's age at a particular time. Do not use at age alone.

She is of age to vote.
He moved abroad at age 21.
Children of school age need regular exercise.

Choose the pattern by meaning

These forms are not interchangeable. Choose the construction by meaning, not by which preposition appears most often.

1
of age

Meaning legally old enough

Use of age after a form of be to say someone has reached the legal or required age.

You must be of age to enter the club.
All applicants are of age under local law.
2
at age + number

Talking about a specific age

Use at age followed by a number to describe something that happened at that time in life.

She started university at age 17.
He retired at age 65.
3
of + age group

Describing a category by age

Use of before an age-related noun phrase such as school age or working age.

The programme supports children of school age.
Many people of working age are seeking jobs.
4
at the age of + number

Formal way to state age

Use at the age of followed by a number in formal or careful writing.

She published her first novel at the age of 25.
He learned to ski at the age of 10.

See the difference in context

The same subject can take different constructions because each sentence answers a different question.

Construction
Example
Meaning
of age
You must be of age to buy alcohol here.
Means legally old enough.
at age + number
She became a manager at age 30.
Refers to a specific point in a person's life.
at age
He graduated at age.
Not idiomatic without a number or modifier after age.
at the age of + number
He moved to Canada at the age of 12.
A fuller and slightly more formal version of at age + number.

Common mistakes

Some combinations appear in real text but do not mean what learners often assume.

Using at age without a number

At age normally needs a specific age after it.

✕ She got married at age. ✓ She got married at age 24.

Confusing legal age with a specific age

Of age means legally old enough, not simply a number of years old.

✕ He started school of age 6. ✓ He started school at age 6.

Adding of after at age

Do not combine the short and long forms.

✕ She retired at age of 60. ✓ She retired at age 60.

Quick practice

Choose the expression that matches the intended meaning.

1. You must be ___ to sign this contract.
2. She won her first title ___ 19.
3. He learned to read ___ five.

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Frequently asked questions

Is at age correct English?

Yes, but it is normally followed by a number, as in at age 16.

What does of age mean?

It means legally old enough for a right, duty, or activity.

Can I say at age of 20?

No. Use either at age 20 or at the age of 20.

of, about, against, to or for racism? of, about, for, in or on friendship? of, about, for, on or to thing? of, about, for, to or with sex? of, about, on, to or for moon? "of access" or "with access"? "of accommodation" or "for accommodation"? "of accuracy" or "for accuracy"? "of action" or "in action"? "of actor", "with actor" or "by actor"? "of address" or "to address"? "of administration" or "in administration"?

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