How often do you need to do exercise as a teenager?

Best - every day: Not just for teenagers, but for all people who wish to remain optimally healthy. Exercise may simply be taking a 20 minute walk at a brisk pace. It is so important for your systems to function properly. The increased blood flow, the increased heart rate, muscle activation and strengthening, joint flexibility, increased breathing rate and volume, etc. Too many obese unhealthy people. Start young !!

60 minutes daily: Most of the 60 minutes should be either moderate activity or vigorous intensity physical activity, and should include vigorous-intensity activity at least 3 days a week. Hope it helps.