Fitz may well be too young to have had his first transformation. It would be entirely in-genre for such curses to remain inactive "until his 18th birthday"...or 16th, or 21st, or whatever is particularly significant. As far as Tera West's possibly unconventional parenting style, it's worth remembering that she isn't human, and lost her mate, who was human, several years ago.
One thing to remember is, according to the curse, it's almost certain that West and MacFinn had a child. Since we know that they never married before MacFinn's death, that child would be a bastard. Fitz means bastard. He has physical characteristics that resemble Tera West and MacFinn, acts in a semi-wolfish sort of way socially, and we apparently have a WoJ that Fitz is cursed. These are rather a lot of factors to dismiss in order to claim it's a coincidence.
I realize JB's also said that he had no plans to use Fitz as a character again, but you never know. That doesn't contradict any of the above; it could mean that JB doesn't plan to bring the Loup-Garou curse back into the plotline. This makes sense--the Loup-Garou curse was covered in FM, and if it originated from Saint Patrick (who was a bloody idiot, if so), then it doesn't seem to be an integral part of the long-term plotline.