They aren't huge as far as freshwater eels go. My understanding is they get to the 12" mark quick enough, then grow really slow from there. I doubt they'd ever get 2 feet though. It also depends on how much ou feed and water temperature. Keep the water a little colder it'll slow them down quite a bit.
55 would be pushing it but maybe ok. If in 2 or 3 years he is too big would you be willing to get a 125 gallon tank for him?