How much to feed adult short-tail

[Jezabel]

He's born around june 2001 and he's now over 5 ft. I feed him a jumbo rat about every 3 week, sometimes every 4 weeks and he's still growing like mad. I know it's impossible I'm over feeding him but every care sheet said them usually max at 5 ft for males. Don't worry, I'm prepared for a big snake (he already has a 5 x 2 x 1.5 feet enclosure) but I wonder since they have such slow metabolism how much an adult should beed feed. Here's a recent pics of him. I don't want to under feed him either but I weight him often and he's still gaining alot of weight

So I'ld like to heard about your feeding scedule.