When you say the age of someone or something, you can say subject + is + # years
▶️ I’m thirty years old.
▶️ That boy is fourteen years old.
▶️ These houses are 200 years old.
When you want to say the age before the subject, then use #-year-old:
▶️ My twenty-year-old sister
▶️ A fourteen-year-old boy
▶️ The 200-year-old houses