Why's my female so small?

I purchased my ball python from Petsmart (unfortunately) on April 5, 2018, so I've had her for over four years. She's a full grown adult, but I was finally able to sex her for the first time today, and she is 100% female. Only thing I'm curious about is that she's only about 37-38" long, 2.3 lbs, which I'm reading isn't normal for adult females. Is this actually normal, or is she just a small baby? I attached a recent photo of her, she's super healthy, has full sheds, lives in a 40 gallon, and eats medium rats.
https://ibb.co/vwFFfvB

How often are you feeding her?
What kind of temps are we looking at in her enclosure?
These are also factors that can affect growth.

Not every snake will exist by the same standards that we place for them. I have a male that averages around 2300g. Even when we want them to be a certain size, they don't always play by those rules. I have a female who was born in 2017 and she didn't hit 1500g until last year. She's actually grown a bit more after laying a clutch last year as well. So she was a slower grower than my other female who hit the same weight in 2 years.