Re: 8 years old or 8-year- old? It depends. In a sentence like My son is eight years old
you have a "normal" number plus plural noun construction.
but in a sentence like I have an 8-year-old son 8-year-old functions as a single chunk, and is an adjective. You could replace it with eg I have a young son.
Because it's an adjective it's not pluralised, and because it must be considered as a single chunk, it's hyphenised. |