Daniel,
They can reach those lengths in a year but usually that with someone trying to hurry and get it big enough to breed. Usually with pet burms they reach around 6-9 feet in a year. I also feed all mine in the enclosures as I feel its much more dangerous moving a large snake thats in feeding mode. Your parents may approve now but may change there mind when you have a 14 foot animal that leaves elephant size poo in there house. Or when they can walk into the house and smell that the snake just pee'd.
There amazing animals and I love mine to death and would not trade them for the world but they are not for everyone.