They are also called third molars because they are the third set of molars to erupt through your gums. The first set typically appears between ages 5 and 7. The second set of molars appears right around the onset of the teenage years. The final (third) set arrives during a person's late teens or early twenties. Historically, this final set arrives at an age associated with a person having "wisdom" - which is why they're called wisdom teeth.