To the OP they get to 17" just to let you know I've seen monsters before.
I'm not kidding you at aquarium adventure in shaumberg whoever is local in the Chicagoland area they have 3-4 monsters in there. It's a huge tank I'd say 1000 gallons or so and easily been there for 6 years or so.17"?? They get big... But no where near that unless exposed to gamma rays.