FAST!
I purchased my Jardini at 5-6in, and thin/wide as a butterknife.
Within 3-4 years he attained a size of 16-18 inches and 2lbs 4oz.
This was with a varied diet of silversides, market shrimp, all types of insects, pinky mice, and an occasional lizard.
Almost forgot, this was a 125gal tank. Had he had a bigger tank, I'm sure he could have done a bit better.