Full disclosure: Both of my children used pacifiers, and as a family we were all very happy about it. It enabled my husband and me to go out to restaurants when our kids were infants, and it was an easy way for our children to be soothed. Pacifiers have even been shown to have a protective effect against SIDS (Sudden Infant Death Syndrome).
That being said, I do believe that 9 to 12 months is a good age to abolish the habit. At this stage, babies are perfectly capable of finding ways to soothe themselves. They are interested and aware of their environments and much more skilled at calming themselves down with simple distractions like engaging them with a song or a new toy. In addition, this is the stage when speech is developing. How can a child speak with a pacifier in her mouth?
Many parents will ask me, “What should I encourage, thumb sucking or a pacifier?” It’s not the parent’s choice. You can offer the pacifier, but you can’t force it. Some babies take to it and some don’t. And thumb suckers will always find their thumbs on their own. Breaking that habit is going to be harder, though!