My kids both quit taking a pacifier early on (3 months of age), probably because they were breastfed. But it is a great question to want to know how old is too old to use a pacifier.
When should my baby stop using a pacifier? | BabyCenter
The American Academy of Pediatrics suggests using a pacifier for the baby's first year of life. Just remember that when you take it away, you need to provide another way for the baby/toddler to self-calm. It might be thumb sucking, holding a fuzzy toy, or listening to soothing music.