Pediatricians usually recommend weaning off the pacifier after a year or eighteen months, because it really can affect how the bite develops and how sounds are pronounced. By eighteen months you should start gradually, though it's not critical if you do it carefully - don't just take it away suddenly, but introduce other ways to calm down (a toy, a word, a routine without the pacifier). The main thing is not to drag it out: the longer you wait, the harder it'll be to let go, because the habit just gets stronger. You could try limiting its use at first - only before bed, then only on certain days, gradually cutting back.