The 35-year-old teacher has been teaching us math for ten years.

35-year-old 是由数字 35 和名词短语 year-old 组成的复合形容词。year 表示"年"，old 表示"年龄"，中间用连字符连接表示"...岁的"。35-year-old 整体作为形容词使用，意思是"35岁的"。