Can you guess her age?

Question
I bought boo boo at a pet store (in Canada), i asked for her age but no one knew her exact age, all they said is that they dont keep rats who are over 6months old. I do not believe this because the way she acted and her mature body looks to be over that (dont rats stop filling out and growing at the age of 6months?).

Anyways she hasnt changed much apart from her coat, she is rusting on her dark patches on her back and chest. This started happening in January. I got her in August 07, so i have had her for roughly 8months.

I know that it is very difficult to just guess and not actually see the rat but i heard that rusting is a sign of old age, i also heard that it could just be genetics.

So, got her from pet store 8months ago, staff said they dont keep rats over 6months so lets assume she was 6months when i got her. So she should be 1year and 2months old, does rusting happen at this age? The rusting is climbing up her back and her DARK grey patches have faded (she is hooded). She is on a total complete diet and no skin problems.

Answer
Rusting can happen at any age, I've seen rusting on 12 week old babies. Rats can and will continue to fill out and grow up to about 8 to 10 months, sometimes even later depending on the individual. Females particularly can be late bloomers. My males are generally done growing by 6 months, but not always.

As for why the rusting is happening; be sure to have her checked for internal parasites - thats part of the cause. If that comes back clean, its probably just her genetics, and nothing to worry about.