They vary drastically and not all snakes will grow to their average length either. I have a six year old female that is 3.5 feet and a male that is a year and a half old and already sitting at 2' 10'' so you never know. I have a good feeling my male will definitely surpass my female in length and weight. I don't worry about it really because they are both in perfect health and I have everything in their tanks set up just as they need them. As long as you have temps, humidity, and housing set up correctly and your baby is eating on a fairly usual schedule there's no reason to worry.