As a tech writer in my younger life I had to be acutely aware of the hyphen. For example, 5-year-old boys are an unspecified number of male youngsters each 5 years old; while 5 year-old boys are 5 boys, all one year old.

However, 5-year old boys are an unstipulated number of aging men; each having, for example, tenure of 5 years.


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