It takes roughly about two years for a new joiner to become JF/O (Junior F/O), In the last 2 1/2 years, about 45 F/Os were promoted to become Captains, but in 1997, there were about 50 guys in a year.
Right now there are about 500 F/Os (including JF/Os) on the seniority list, if your arithmetic is not too bad and you are an optimistic person, it seems to me 12 years is a very optimistic guess.