I have a female mojave that was born August 2014. She weighs 206g. I have a female that was also born August 2014 and she is 890g... so it is very hard to tell by weight, age and size.

Breeders tend to feed snakes they do not plan on keeping a little less then their keepers, so they are usually smaller then an average fed BP. But, many in my collection were about 6-8 months when they were 400-500g on average. That is not a guarantee though and you may never know your snake's true age. And as stated before, she is not a mojave.