Nice hypo. There is no way to really tell the age as they all grow different and also based on feeding to an extent. I have an almost 6 year old normal BCI girl who is about 7 feet. I also have an early 2014 sunglow female who is about 6 feet. Then i have a couple who are just over 2 years old and just over 3 feet. If any of that info helps you in maybe trying to guess an age on your snake.
Also, get that poor guy out of that fish tank and into a nice PVC cagesAnd my vote goes to AP cages even though they take forever and a day to get but are well worth the wait.