If a tooth grows at age 20, the first thing you should check is which tooth is growing. If it is the most common wisdom tooth, it is a normal physiological phenomenon. As the last tooth to erupt, the wisdom tooth itself begins to erupt around the age of 18-25 and is also known as a wisdom tooth because it erupts just in time for the adult stage. So if the tooth that grows at age 20 is a wisdom tooth, it is a normal condition that indicates that all the teeth are starting to erupt. However, if an abnormally ectopic tooth erupts at age 20, it is a cause for concern. For example, if new teeth start to erupt in the front of the mouth at the age of 20, it is recommended to go to a professional dentist as soon as possible to check for the appearance of multiple teeth.