I got mine at a smaller size, but they went from 2"-12" in the first year, then it slows down. They can make it to 16"+ after 2 years.
Some reach 20", but that seem to be rare; 16-18" is a bit more common.
Here are some in-tank shots after two weeks. They are eating prawns twice a day and seems to be settled well. They are out and swimming around when nobody is there but as soon as I enter the room they go in to hiding. Thanks for all the advise from the experts. Will keep this thread updated on their growth. Oh, by the way I went back to LFS two days after I bought them and got another two. Now I have 6 in total.