Chicken age

[goodag2]

I was wondering how old my hens have to be before they start laying. I found the answer to that question but then I got to wondering if there is a way to tell the age of a hen. No one seems to know how. I raised one of mine from a chick but I got the other one after she was grown-looking. Also, she doesn't have much of a comb and what she has is more black colored and definitely not red. She is supposed to be a black australorp.
Ain't this fun!

 

[siz8003]

I have no idea but a pic might help