I would say that a child is too old for a pacifier when they turn 2 to 3 years old.
After 1 year old the child really does not need a pacifier but if the pacifier keeps the kid calm and relaxed and also helps the child sleep then I would have no issue with a a child having a pacifier until at least 3 to 4 years old.
But by 4 years old the child should not be using a pacifier especially in public because not only is the pacifier bad for the child's teeth the child can get made fun of in public when using a pacifier.
And also the child cannot take a pacifier to school.
Well I do remember as a kid a 5 year old boy in Kindergarten came to school with a pacifier and for awhile he was not made fun of.
But eventually he came to school in 1st grade and then the first grade children made fun of him.
So he threw the pacifier away and that was the end of that.
But I would not want to send my kid to school with a pacifier and have them made fun of.
At home I would probably be fine with the 5 or 6 or 7 or even 8 year old using a pacifier in the day or night but not in public.
But the pacifier should really be taken away by age 2 to 3 years old.