I'm sure you'll get mixed opinions on this one! I personally think it can affect how their teeth grow in, so if your lo still uses one you might want to think about weaning to just night time use at least, and eventually so that he doesn't need it at all.
That being said, I know lots of babies 18mo and older who still use them. It's really a personal choice as to when you'd like to wean the baby! You might want to talk to your doctor or a dentist on the affect it will have on his teeth.
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