How old is my child?

Relax. I knew with google in my hand, I could figure out anything. Recently, I was confused on how old is my daughter. Do I count by the month, the day, the hour? I thought she was 18 months old and argued with the lady who told me otherwise. Then I found this:

http://www.calculator.net/age-calculator.html

She is only 17 months old. That is what I get for trying to let her grow up too quickly.