If someone’s age is being described and there is no noun that is being modified, there are no hyphens.
…He is five years old.
…She is 55 years old.
When the combination becomes a direct adjective (right in front of the noun), it is hyphenated. In this case, we say “year” instead of “years.” That does not make a difference to the punctuation.
…Charlie is a five-year-old child.
…The patient is a 55-year-old adult female.
When the combination is a noun, it is hyphenated because “-old” is a combining form.
…The five-year-old was not injured.
…The victim was a 55-year-old male.