In fact, it doesn't fully mature until around the age of 25 - around the time you finish university and are ready to start working. Anything you do before then will affect the development of your brain, for better or worse.
Drugs and alcohol are some of the most harmful, but also the most common, factors that disrupt the development of the teenage brain. The ability to think, concentrate, learn and remember is all affected in teenagers who have used alcohol Despite the harmful effects of early substance use, substance abuse is very common in schools and among adolescents. Studies show that by senior year, "nearly 50% of adolescents have tried an illicit drug. And that's just the beginning. About 66% of teenagers have also consumed alcohol by the end of high school".
“Drug Abuse in Schools: Drugs in High School.” Turnbridge, 26 Jan. 2021, https://www.turnbridge.com/news-events/latest-articles/drug-abuse-in-schools/#.
Omelchuk, Konstantin. “Complete Life Cycle of Person`s Life. A Baby, a Child, a Teenager, an Adult, an Elderly Person. Vector Illustration Cartoon Style Stock Vector - Illustration of Grandfather, Human: 112173304.” Dreamstime, 18 Mar. 2018, https://www.dreamstime.com/complete-life-cycle-person-s-baby-child-teenager-adult-elderly-vector-illustration-cartoon-style-childhood-to-old-age-image112173304.