FWIW, IMO he'll get bigger than 5"-6", but it will take a at least a few years and I'm sure you'll have a variety of BIG tanks by then.

My guess would be around 8"- 9" total length.
I'm curious as to whether the pattern will stay or not as claimed. It doesn't look as much like a S. angelicus pattern, but more like the young S. eupetrus pattern, which eupterus grow out of as they grow up. My vote is that he becomes more spotted than stripey as he matures.