Or, if you find you become attached to him, you can just get yourself a really really big tank! . Think of all the pretty fishes you could have! .
I might be wrong, but I have a feeling he's a Common Plec - and they do become pretty sizeable eventually. They do seem to be a bit lighter when they are young. When we first bought Dyson, he was lighter than he is today. He darkened up once he had settled into his tank, too. And like Sharn said, perhaps there are subtle differences in the cats available up your way.
I'm guessing your LFS was a bit vague over what kind of plec he is? It'd be good to know how big he grows for certain - although I think he is going to be a biggie .
They do take a wee while to grow that big, though - so there's plenty of time to start planning for that 6 foot tank now! Go on, you know you want to! :lol: