Final answer:
Teenagers should stop drinking when they reach the legal drinking age to protect their developing brains and overall health.
Step-by-step explanation:
Teenagers should stop drinking when they reach the legal drinking age, which is typically 18 or 21 depending on the country. It is important for teenagers to wait until they are of legal age to consume alcohol because their brains are still developing and alcohol can have negative effects on their cognitive function and overall health. Additionally, excessive alcohol consumption at a young age can increase the risk of addiction and lead to a range of physical and mental health problems.