TSN is a genus of multiple species, each with their own max size. The genus seems to be in a taxonomic limbo though, which doesn't help - some scientists state there are 8-9 species, others say 3 or some such.
P. fasciatum seems the most common in the trade and doesn't exceed 3 feet or not by much.
Yes, we usually get junk TSN in our trade, refuse from the farming operation of food TSN and carelessly and cheaply raised ones for ornamental purpose.
Going back to the OP, and average TSN should reach 1.5 feet in the first year. It will far outgrow a 55 gal tank. By the time it reaches a foot or even before that, it will have eaten the raphaels.