做表语的话,就是one year old,如：she is one year old now.
作定语的话,就是one-year-old.如：she is a one-year-old gilr.(这里要注意,one虽然是以元音字母o开头,但是其音标不是元音,所以不定冠词要用a而不是an）
还要注意的是,“一岁半”,要说成one year and a half,或者one and a half （years）!
year的单复数,取决于half的位置.
祝进步!