Hi Psix, You are referring to a compound adjective. Compound adjectives are a group of words that function as an adjective which provides more information about something/someone (noun). In your example, thirty-year-old is a compound adjective describing the age of a person (noun). Therefore, you cannot write thirty-year-old without having a noun behind. Other examples of compound adjectives include: sweet-smelling nectar (noun), handsome-looking guy (noun) etc. If you still prefer not to use a noun, you can rewrite the sentence as: Mr Li is thirty years old this year. Hope this helps. Cheers, Lance