Numbers to express age
Age is always shown as a numeral except when it begins a sentence.
She is a 35-year-old mother.
She has a 2-year 6-month-old toddler and a 4-year-old child.
As in all cases, it is preferable to recast the sentence (if possible) to avoid spelling out numerals. With ages, this can frequently consist of adding an article.
A 7-year-old boy
This 21-year-old woman
Use hyphens to form a compound modifier when necessary. (See Compound Words and Hyphens - rules for compound modifiers apply to numbers, as well.) Use the hyphen whether the modified noun is expressed or implied.
The patient is a 21-year-old woman who presents
The patient is a 21-year-old who presents (implied)
There were 13-year-old children at the party
There were 13-year-olds at the party (implied)
Do not use a hyphen when the numeric age is not used as a compound modifier.
The patient was 15 years old at the time of his injury.
She was 25 years of age at the time of her first miscarriage.
When an age is shown in terms of decades, instead of a specific number, it is not preceded by an apostrophe. There is no apostrophe after the s.
He appears to be in his 50s.
She was well until her 30s.
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