At what age should we correct our toddler if s/he is still bulol (stutters)?

For me there is no such thing as to what age should we correct our toddler's way of speaking. From the moment they started to imitate the words we speak, whenever we heard them incorrectly, we should try to correct it already. And besides, we shouldn't be talking"baby talks" to them, instead we should talk and pronounce the normal way, like they're already mature people.