Your teen's brain is still developing. Binge drinking is extremely harmful to brain development. It affects later cognitive and emotional functioning.
https://www.niaaa.nih.gov/publications/alcohol-and-adolescent-brain
More and more research suggests that drinking alcohol in adolescence may have significant effects on brain function. The earlier people start drinking alcohol, the more likely they are to experience a measurable impact on cognitive functions, memory, and school performance over time—perhaps even into adulthood.10,11
Alcohol misuse during adolescence—generally measured by a history of binge drinking or alcohol use disorder diagnosis—has been linked to changes within and between brain regions.12 For example, researchers have found reductions in the size of the frontal lobe (involved in planning and decision-making), hippocampus (involved in learning and memory), amygdala (involved in fear-sensing), and corpus callosum (involved in the communication between the two sides of the brain).10,13 Researchers have also found that heavy drinking changes the normal developmental patterns in the connections between and within brain regions, and weakens connections between brain areas that regulate emotional and cognitive functioning.4,13