we used to have one at the fish store I used to work at in our 1,500g. circular tank he was every bit of 20in. long he was at least 7yrs. old when we got him I think we had him for at least 6-7 more yrs. before he died but he was at LEAST 18IN. LONG
Mine has been growing very....very slowly as well. I got mine last October and at that time, it was about 4.5" in length. It's up to about 6.75" now. I also feed it a strictly carnivorous diet, consisting of bloodworms, krill, plankton, and beefheart.