The phrase "one's teenage years" refers to the period of time in a person's life when they are between 13 and 19 years old. This is typically considered a transitional phase, where individuals go through significant physical, emotional, and cognitive changes as they transition from childhood to adulthood. During this time, teenagers often experience increased independence, self-discovery, and socialization, while also facing new challenges such as peer pressure, academic stress, and identity formation.