Yup, like mentioned, literally impossible to tell. She could be a year if someone hardcore power fed her, but she could be older. I have an 11 year old ball python that is 3.5' and 1,400 grams, probed female, but not 100% convinced on that since it was my first probing on my own. I may see if the person caring for him/her will have them probed to see for sure. But, I only know the age because I got him as a hatchling in 2006, I don't know his exact birthdate, so he could be several months older than I think he is.

Feeding regimen and genetics impact so much that there's no way to tell. Even within the same clutch, each individual will grow at their own rate, and end up at different sizes. All we can say is your beep is an adult. haha