tap into google, lots of info, heres a snippet

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A sweet sixteen is a traditional birthday party for girls to have when they turn sixteen years old. In parts of the United States and Canada, sixteen is the age at which one may obtain a driver's license. It is also the age of consent in many states, hence it is viewed by many adolescents as an important milestone. It is the American counterpart of the Spanish and Latin American tradition of a Quinceañera, with both parties having the same sense but in Spanish-speaking countries it is at the 15th birthday.

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