Yeah, they will get big fast. Might start to slow a bit at 12" (maybe 3/4" a month or so). Large tank at that point will help growth.
They ultimately will get to about 18". But one thing about fish. They never really stop growing. Especially monster fish.
My male hit about 16" in a year and a half. When he died at about 6.5 years he was 18-19".