While some babies are born with teeth, most infants begin to have teeth erupt during the first year of life. The average age of completion of eruption of all 20 primary teeth into the mouth is 30 months. For most of us, the first permanent teeth to erupt are the first (6 year) molars. They come into the mouth behind the last primary tooth in the arch and do not replace a primary tooth. The first primary tooth lost and replaced with its permanent counterpart is the lower primary central incisor at about age 7. From age 7 to 11 or 12, primary teeth are lost and replaced by the permanent teeth. The last teeth to erupt are the third molars (wisdom teeth), which frequently appear around age 18.
As a generality, having the teeth erupt in the proper sequence is more important than the timing of the eruption, whether early or late. When teeth erupt in the correct sequence they are more likely to achieve proper placement in the dental arch.