Before I had my son, I would run into adorable children on the street and ask:
"Aw! How old is your son?"
And the mother would reply:
"He's 19 months."
At that moment I would internally roll my eyes and laugh. 19 months? How old is that really? When you ask an adult how old they are they give you a regular number: "I'm 30." or "I'm 45." And they are referring to years and not months. I wasn't used to hearing age referred to in months. I promised myself that I wouldn't be one of those parents that referred to their children's ages in terms of months.
However, now that I have a child times have changed. Up until my son was one year old, I referred to him in terms of months. He was at one time seven months old, then eight months etc. until he turned one year old.
My son turned a year in May. Now that it is June he is no longer exactly one year old but rather....13 months!! I know, I swore I wouldn't do it. But the truth is, developmentally, from child to child, there is a vast difference from month to month.
There is a significant difference between a one year old and a 13 month old.
On the other hand, I (as an adult human being) cannot refer to myself in months. It would be socially unacceptable and bizarre to say that I am 355 months.