if that's what the Internet says, it must be true.
Seriously though, these eels typically will only grow to what size their enclosure allows. My fimbriated eel was supposed to grow to 3ft, but it never really got past 20in or so in my 75gal. Another example is a black caiman which can grow to 12ft in the wild. My friend kept one in a 55gal tank for years and years and it never grew larger than 2ft. It seemed to stay a baby forever. Its growth was obviously stunted. When he sold it to a guy that has a huge outdoor pond, it grew from 2ft to 8ft in about 2 years. I guess it was playing catch-up for all those years that it was stunted.
Basically, what I'm saying is if the 55gal seems big enough for it now, then hopefully it will not outgrow the tank.
IME, most fish/reptiles will only grow to as big as their enclosure can support or accommodate.