It can get to those sizes with 12 to 16 months all depending on which species of atf u have. Most get from 3 to 4 inch to 12" within a yrs time maybe slightly longer or sooner all depends upon how u feed them, pellets and frozen once a day or so or a constant supply of feeders 24/7. U can keep other fish as well with them like non aggressive cats such as a tig or irwini....I have mine in a 1500 gal fiberglass tank with a few tank mates. Hes taken a few fish as well. I have a post on this forum if u go back a few weeks u will see it. Gatf update....vatf and their like I've seen up to 20" or so, gatf 4 feet more or less. Could be larger ones out there but not many have gotten to the size mine is. To raise atf to adulthood u must be patient, consistent and disciplined. Whatever u believe goes out the window. These are game fish not tropical fish like a discus or Guppy!