How long does it take for teeth to grow fully?

From eruption: In the mouth(when you first see the tooth) to fully formed root-3 years.

3-9 years: Teeth form under the gums and eventually about 1/3 of the tooth erupts into the mouth. Root formation continues under the gums. Baby teeth can be fully formed in as little as 3 years. Permanent molars can take up to 9 years to form. For example 6 year molars are already beginning to form at birth, and don't fully mature until about a year after they erupt.