They grow 2-3 " per month. Think of them as jumbo sized tinfoils. They eat just about anything, constantly move and grow rapidly. I had a couple that I gave away but really enjoyed them.
Yea, these things are beasts, I had 4 of them at about 14 inches . They went nuts once during feeding and broke my middle piece in my 190g.... and before I could drain it the seal cracked .
I've seen them in zoos, had to be 2 feet at least.