1
My nephew is five years.
My nephew is five.
My nephew is five years old.
To say someone’s age after the verb be, use number + years old: ‘My nephew is five years old.’
We can also use only the number: ‘My nephew is five.’
Do not use number + years without old.
2
An 80 years old woman disappeared at the beach.
An 80-year-old woman disappeared at the beach.
Two-years-old children shouldn’t go to school.
Two-year-old children shouldn’t go to school.
Before a noun, use a compound adjective with a number: number-year-old + noun.
Join all the words with hyphens and keep year singular: ‘an 80-year-old woman’, ‘a two-year-old child’, ‘two-year-old children’.
We use the same pattern with other measurements: ‘a two-day trip’, ‘a 30-minute lesson’, ‘a ten-kilometre walk’.
3
Two years olds like to be independent.
Two-year-olds like to be independent.
We can also use number-year-old as a noun: ‘I have a five-year-old.’ ‘Two fifteen-year-olds entered the competition.’
Join the three words with hyphens, keep year singular and add the plural -s to old: ‘one five-year-old’, ‘two five-year-olds’.