Ive seen them reach 36" but thats rare...24" is common. One of the lfs in Phoenix has a long interconnected series of tanks with about 50 of them in it
I don't know the exact size but the place is HUGE and they are kept in a series of 300 gallon tanks (best guess) connected by large acrillic tubes. I think I counted 10 tanks in all.
how long will it take them to get to 30"? To be honest I phoned lots of public aquariums and they said most of theres are around 25" and only a few have gotten bigger, and they have them in MASSIVE tanks. my smallest one is 17" and the biggest 20"-22"