If you're younger than 20 but older than 12, congratulations! You're a teenager!
Teenagers are also known as teens or adolescents. Generally, teenagers have finished elementary school, are growing fairly quickly, and are in the last stage of development before they become official adults. As a teenager, the things you may do include graduating from high school, getting a driver's license, and working at a paid job. Before teenager was coined in the 1920s, the word was teener.