How to properly answer an "Age" field in a form? [closed]

Which of the following is the most correct to use?

Age: 13 years old

Age: 13 years

Age: 13


Unless one is filling out a form to register an infant for something, the number alone would be adequate. If for an infant, you might need to say 6 months, 18 months, etc. With regard to your school project interview, you would first review your project requirements to see if they specify a format for the age. If they do not, write it as 24 years, 48 years, etc.