I think the biggest problem of young people in the 21st century is technology addiction. Because of technology addiction, some young people waste many hours on their phones or computers every day. During this time, they could study for their lessons or do enjoyable and healthy activities like playing basketball, walking, or spending time with their friends and family.
Technology addiction also causes many health problems. These problems include sleep problems, low energy, eye pain, and obesity. When young people use technology too much, they feel tired and unhappy. If they use their phones less, they will probably feel better and healthier.
In the past, young people were healthier because technology was not very common. They played outside more and used their time more wisely. Today, many young people cannot manage their time well because of technology. To be healthy and successful, young people should use technology correctly and for limited time.