By being an adult and forcing myself to do things I often don't want to because I know time won't wait for me. Getting to heaven is hell and your brain will resist change in lifestyle until that change becomes your lifestyle. Most people aren't distracted by ass and films because they have ADHD, they're distracted because those things don't require anything but passive consumption and they lack discipline. "I can't concentrate," often boils down to, "I have no discipline."
Speaking in general, most adults are fully capable of focusing. We choose daily what we find most important to focus on. For some it's studying six hours for another I.T. certification. For others, it's a six hour Netflix binge. We all have passive hobbies we enjoy and no man is better than the next in that regard. When you struggle to prioritize effectively (at least to your level of personal satisfaction) you have to consider that it's less about your capability and more about your willingness.