Years old or years of age
Incorrect : My father is fifty years.
Correct : My father is fifty years old. Or My father is fifty years of age. Or My father is fifty.
Note: When you say the age of a person, you can use any of these three correct expressions. But in case of other things, you should use only the first formula. For example:
This building is fifty years old.
You cannot say:
This building is fifty/fifty years of age.
