I have had one for over 2 years, got him at 4", it grew very fast to 10" and then very slowly for a year, the last few months he has been growing faster and is now around 14-15".
You can see pics from when i got him here:
http://www.monsterfishkeepers.com/forums/showthread.php?t=81417
and a more recent pics:
You can see pics from when i got him here:
http://www.monsterfishkeepers.com/forums/showthread.php?t=81417
and a more recent pics: