L18, L177, L85 and LDA60 are now all considered to be the same species, Baryancistrus xanthellus. In the past it has been quoted that some varieties get bigger than others (IIRC L18 was the one that grew to over 12", L177 was a bit smaller), so you'll have to try figure out which yours is. I think L177 has larger spots and larger gold margins, certainly looks like it in this picture; http://www.planetcatfish.com/catelog/image.php?species=baryancistrus_xanthellus&image_id=4957
Will it get to 12"?? Possibly, but it will take a long time, a good sized tank, and good food. IMO you should ditch the coarse gravel in the pic (looks massive if that fish is 4"!) and replace it with sand as I've found my plecs (including Baryancistrus) will graze on all sorts of food sitting on the bottom, including flake and small NLS granules. With the coarse substrate that kind of food will end up out of reach of the fish.
Check out the species profile on planetcatfish: http://www.planetcatfish.com/catelog/species.php?species_id=153